and merge duplicate parts

Related to T3829

This fixes warning like [1] and attempt to fix the build [2]

[1]
```
16:47:16  /var/lib/jenkins/workspace/DDOC/build-on-diff/swh-docs/user/faq/index.rst:41: WARNING: hardcoded link 'https://archive.softwareheritage.org/save/' could be replaced by an extlink (try using ':swh_web:`save/`' instead)
```

[2] https://jenkins.softwareheritage.org/job/DDOC/job/build-on-diff/59/console

we will need to fix this later on.

It's mandatory to use :swh_web: instead of archive.s.o since
sphinx 4.4.0

It's mandatory to use :swh_web: instead of archive.s.o since
sphinx 4.4.0

This also drops spurious copyright headers to those files if present.

Related to T3812

Related to: T3533

Related to T2400

This has been broken [1] for a while.

[1] https://jenkins.softwareheritage.org/view/swh-draft/job/DDOC/job/dev/311/

Related to T3780

Related to T3717

Closes T3737

the 'architecture' section has a bunch of items not useful to newcomers
(Keycloak, mirroring, ...)

Related to T3621

Related to T3154

Related to T3154

This moves the dns setup out of the networking page into its own section.

Related to T3154

This splits the existing pages into multiple ones:

- (new) reference-setup.rst: This is the main page filled in with the existing one
- (update) howto-test-changes-in-vagrant.rst: reference link got updatee to the current
  readme section)
- (update) howto-manage-third-party-modules.rst: coming from the main page with links
  broken fixed
- (update) howto-deploy-puppet-change.rst: coming from main page with links broken fixed
- (update) tutorial-my-first-change-in-puppet.rst: With some actual updates on how to
  develop, diffing and asking for review.

Related to T3154

Related to T3154

Related to T3154

This splits the upgrade swh services from the intranet page in 2 distincts
documentation.

Related to T3154

The default credentials for dell and supermicro have been installed in the creds store.

Related to T3154

There is no need for it here. This keycloak doc is about its use, not really an
architecture page.

Also, it's currently failing the docs dev build.

[1] https://jenkins.softwareheritage.org/view/swh-draft/job/DDOC/job/dev/6866/console

Related to T3154

This also:
- installs redirection from old location to the new one.
- install the intended audience on respective documentations.

Related to T3154