Merge with upstream GitLab 14.1.0 and adaptation

First iteration, passes functional tests with `--heptapod-remote` and
those with `-m fs_access`. Comprehensive RSpec run to be done by CI.

Various notes and things to test manually:

  - Admin area: help messages about user approval/ban/delete/reactivate have
    switched from HAML templates to VueJS.
  - the rename of project services as integrations (same terminology
    as in the UI) is complete.
  - same remarks as in merge of 14.0.0 (eaf3be02fbc4) in the heptapod-stable
    branch, since they were done independently.

Things to solve:

  - RSpec tests: still have process management issues for the HGitaly
    server, CI should not be affected (server is spawned separately,
    not by `TestEnv` class)
  - `gdk start rails-background-jobs` does not work for me, but
    launching in foreground from a terminal does.
  - doubts about SSH keys management (sync of `authorized_keys` file,
    but could related with sidekiq not running at the time it was
  - Gitaly protocol upgrade in HGitaly

branch : heptapod
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