Related T918

Related 08121f71

rationale: swh-init.sql should only contain stuff that requires being Postgres
superuser

Summary:
Avoids writing a bunch of temporary files for no good reason. T866 was a symptom
of this.

Test Plan: No regressions in the unit tests

Reviewers: #reviewers!

Differential Revision: https://forge.softwareheritage.org/D282

swh-enums: Reference new mercurial revision type

Related T329

the new sphinx seems to be confused by relative symlinks when we merge
all docs together

was: "swh"

this way we can ship the images as is in the global doc, with minimal clash risks

Summary:
Snapshots are the new, improved occurrences; They're the topmost object in the
Software Heritage Merkle Tree, and represent a full picture of an origin at a
given time.

Snapshots contain a list of named pointers to objects in the Software Heritage
archive, as well as an intrinsic identifier. The full specification is
supported: pointers to all types of objects, dangling pointers, as well as alias
branches.

They're implemented with a somewhat classic fully normalised model; Foreign keys
use a sha1_git, which makes more sense regarding pointing at non-existent
objects, at the expense of some economies of size.

Backwards compatibility both ways with occurrences is ensured: when adding a
snapshot linked to an origin visit, the corresponding occurrences are created in
occurrence_history; when querying the snapshot for an origin visit where we
haven't generated the snapshot yet, a virtual snapshot with id None is returned.
This lets us migrate to the new tables gently.

Close T567.

Test Plan: Integration tests are included.

Reviewers: zack, #reviewers!

Maniphest Tasks: T567

Differential Revision: https://forge.softwareheritage.org/D268

Finalize it really.

Related T873

Related T871

Related T871

Related T871

This adds method 'origin_search' to storage enabling to search for origins
whose urls contain a string pattern or match a regular expression

Related T848

Related T851

Related T851

Due to a new value in db for the same tool.

Related 35253443
Related T849

Related T849

deleting entry points get_all and get_by_provider
creating one unique entry point origin_metadata_get_by

adding entry point provider_get_by name+url

added documentation and new version for schema