flake8 hook has been removed from https://github.com/pre-commit/pre-commit-hooks
so now use the one from https://gitlab.com/pycqa/flake8

- postgresql-server-dev-all was overkill, postgresql libpq-dev suffice
- short description on deps grouped by role

They are needed for the documentation.

- pre-commit doesn't necessarily exist as a system package (i.e.
Debian buster), and is used as a Python library in swh git repos,
so install via pip in the virtualenv.
- install local swh packages as a 2-step process to avoid errors

The lister no longer creates Origin objects.

- add the indexer journal client
- replace the Ceph logo with (Open)ZFS one
- add the MDStorage
- add Vault workers and their RPC link to the Storage and Vault API

Related to T2105

Reviewers: #reviewers

Differential Revision: https://forge.softwareheritage.org/D3634

Summary:
If running this command on bullseye, there may already be a postgresql-12-server
installed; so pytest-postgresql will try to use postgresql-12's pg_ctl, which
does not exist.

Using the virtual package 'postgresql' instead of 'postgresql-11' installs
the right version for the distribution.

Reviewers: #reviewers, olasd

Differential Revision: https://forge.softwareheritage.org/D3631

Reviewers: #reviewers

Differential Revision: https://forge.softwareheritage.org/D3630

This reverts commit b5d50d89.

This only worked because I have a local postgresql on which I'm superuser,
apparently.

This reverts commit 457c9f64.

This commit removed both the source copy step and the actual linking of the docs
sources. Turns out that the latter is "somewhat" necessary for a proper doc
build.

Close T2386

by installing swh packages in standard (non-editable) mode, so we have an
easy to specify swh/ directory in which all the swh packages are installed.

The main drawback of this solution is we loose the possibility of rebuilding
the doc (in tox) while editing a package's documentation without rebuilding
the tox env (i.e. using tox -r). But IMHO this usage has never been
adpoted by anyone, so it's much simpler that way.

Related to T2367

Related to T2367

... for the time being, as swh.scanner is not published on PyPI yet

This reverts commit bdefee74.

Now that sphinxcontrib-images extension has gained support for Sphinx > 2
in its 0.9.1 release, we can remove the restriction on Sphinx version in
the requirements file.

Also considering that we now rely on a virtualenv to build the doc, remove
the hacks to invocate sphinx-build and sphinx-apidoc in Makefiles.

Related to T2264