For now, this only checks they aren't just a string

This only checks the name is a string.

For now this increases code complexity, but this will allow addition
of other check more easily.

The leading newline prevented textwrap.dedent from removing them.

It was never actually tested...

This fixes crashes when running 'pytest -k migration', because swh/deposit/tests_migration/
lacks a conftest to initialize the database.

This will refuse the metadata-only deposit if the metadata provenance does not match.
This is doing a similar check already done when doing deposit with origin url
mismatching that same (client) provider url.

Related to T3677

We don't have much use for it anymore, let's use ElementTree everywhere
for consistency.

This should ease deposit listing in whatever forms (backend db read or client consuming
deposit listing).

Deposit types stand for:
- meta: metadata-only deposit
- code: content deposit

This commit includes a migration schema script which adds a new column 'type'. The
script is also in charge of migration existing data with the right type values..

Related to T3677

Related to T3677

xmltodict was already on the way out for the deposit, and the latest
libexpat security update broke it entirely when dealing with namespaces,
which means we cannot use it until this is addressed.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1006317

Functional changes of this commit:

1. No more writes to the 'metadata' jsonb column in the DB (as it
   strongly depends on xmltodict)
2. ServiceDocumentDepositClient always outputs a list of collections,
   instead of None/dict/List[dict] depending on the number of
   collections (artefact of using xmltodict, which is replaced by proper
   parsing)

No one uses that, and it's redundant, as we provide the original XML

This now lists the deposit with their associated raw metadata if any is present. This
will allow adaptations in the moderation view [1] to display the metadata provenance
url (provided it's parsed out of the raw metadata).

[1] The moderation view consumes this internal api.

Related to T3677

This will be useful for metadata-only deposit, as there is not necessarily
and origin in the referenced SWHID; and even when there is, it is usually
not the actual source of the metadata.

Therefore, we need this new field to link back to the provenance of the metadata.

This commit does not touch the external API though; ie. `metadata_dict`
is still present in the JSON API, and the equivalent `jsonb` field remains
in the database. They will probably be removed in a future commit
because they are not very useful, though.

Rationale:

I find xmltodict's approach of translating XML tree to native structures
to be intrinsically flawed for non-trivial handling of XML, because the
data structure is:

* implementation-defined (by xmltodict, which is python-only) and it may
  change across versions
* does not intrinsically store namespaces, and relies on an internal
  prefix map  (though it isn't much of an issue right now, as we do not need
  composability and all the changed APIs are private)
* not stable; for example, `<a><b>foo</b></a>` and `<a><b>foo</b><b>bar</b></a>`
  are encoded completely differently (the former is a `Dict[str, str]`,
  the latter is `Dict[str, list]`.

And every operation manipulating this data structure needs to check
presence, number *and* type on every access. Consider this part of this
commit for example:

```
-    swh_deposit = metadata.get("swh:deposit")
-    if not swh_deposit:
-        return None
-
-    swh_reference = swh_deposit.get("swh:reference")
-    if not swh_reference:
-        return None
-
-    swh_origin = swh_reference.get("swh:origin")
-    if swh_origin:
-        url = swh_origin.get("@url")
-        if url:
-            return url
+    ref_origin = metadata.find(
+        "swh:deposit/swh:reference/swh:origin[@url]", namespaces=NAMESPACES
+    )
+    if ref_origin is not None:
+        return ref_origin.attrib["url"]
```

the use of XPath makes it considerably shorter; and the original version
did not even check number/type (ie. it would crash if an element was
duplicated).

If the user is providing the `--metadata-provenance-url`, the xml generated will forward
that information to the deposit server. If the user is providing the metadata file
directly, a warning will be logged to notify the user of the missing metadata provenance
url (if it is missing).

Related to T3677

Either is valid according to https://schema.org/docs/gs.html ;
but we need to pick one, as they are opaque identifiers.
And codemeta chose http:// (because it was the only one to be
valid back then), so we should stick to this one.

We don't use that feature at all as far as I am aware.

I also find that it complicates any metadata handling (especially the validation
I would like to add in the near future), and probably does not match semantics
intended by SWORD (merging occurs on PUT requests, as we don't implement PATCH)

Prior to this commit, only rejected deposit were storing problem details. Now that we
can have warnings even in case of 'verified' deposit, we need to store that details for
post-analysis.

Note that this also fixes the docstring of the overall class which were out of date
since the beginning (duplicated from another class).

Related to T3677

This introduces a new check about the metadata provenance. While it's a suggested field,
it's definitely something that we want deposit clients to send us. So warn when it's not
the case. That does not reject the deposit but it's worth keeping that detail in the
backend.

Related to T3677

Related to T3677

Tests still pass and it aligns the test requirements with other
swh modules.

To install the new hook:

  $ pre-commit install -t commit-msg

Related to T3916

It will be replaced by what is currently called 'offset_bytes'

instead of not being detected and crash as an internal server error (500)

Related to T3856

This fixes the build [1] [2]

[1]
```
10:49:23  Warning, treated as error:
10:49:23  /var/lib/jenkins/workspace/DDEP/tests-on-diff/docs/README.rst:40:hardcoded link 'https://archive.softwareheritage.org/save/' could be replaced by an extlink (try using ':swh_web:`save/`' instead)
```

[2] https://jenkins.softwareheritage.org/view/swh-draft/job/DDEP/job/tests/1741/console

The next release of swh-model will remove it from the constructor, attributes, and dict.
However, this keeps using 'offset' despite the removable from swh-model, because it
needs to be JSON-serializable.

It shouldn't be used anymore

They will be used by the deposit loaders in the release message.