Related to T3829

use proper `:file:`, `:command:` and `:envvar:` roles.

using `docker service update --config-add` like commands.

with infrastructure sizing estimations.

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