Until we solve https://gitlab.com/gitlab-com/gitlab-docs/issues/347,
let's just be explicit to avoid confusion.

Signed-off-by: NTakuya Noguchi <takninnovationresearch@gmail.com>

Sidekiq jobs frequently spawn long-lived child processes to do work.
In some circumstances, these can be reparented to init when sidekiq is
terminated, leading to duplication of work and strange concurrency
problems.

This commit changes sidekiq so that, if run as a process group leader,
it will forward `INT` and `TERM` signals to the whole process group. If
the memory killer is active, it will also use the process group when
resorting to `kill -9` to shut down.

These changes mean that a naive `kill <pid-of-sidekiq>` will now do the
right thing, killing any child processes spawned by sidekiq, as long as
the process supervisor placed it in its own process group.

If sidekiq isn't a process group leader, this new code is skipped.

We've previously exposed ca_file and ssl_version but there are many
possible options that can be used inside tls_options. Instead of
exposing individual ones, simply expose the entire hash so it can
be passed in and we won't have to add things in the future.

This brings back some of the changes in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20339.

For users using Gitaly on top of NFS, accessing the Git data directly
via Rugged is more performant than Gitaly. This merge request introduces
the feature flag `rugged_find_commit` to activate Rugged paths.

There are also Rake tasks `gitlab:features:enable_rugged` and
`gitlab:features:disable_rugged` to enable/disable these feature
flags altogether.

Part of four Rugged changes identified in
https://gitlab.com/gitlab-org/gitlab-ce/issues/57317.

As mentioned in
https://gitlab.com/gitlab-org/gitlab-ce/issues/58121#note_145299901, it
wasn't obvious that upgrading an GitLab HA cluster required special
care. Link to the Omnibus documentation for upgrade instructions.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/58121

Signed-off-by: NTakuya Noguchi <takninnovationresearch@gmail.com>

Markdown renderers find it easier to determine
where lists start and end when lists are surrounded
by new lines.

For consistency, also ensure entries in the list
are aligned when they span multipls lines.

- Fix "introduced in" note
- Add missing links
- Remove unnecessary hrs
- Wording
- Feature badge (admin only)

Configuration examples were moved into their own section for the purpose
of organizing and being able to link directly.

Adding password in the Redis Sentinel config does not actually work
because v3.2.x doesn't respond to the `AUTH` command.

This came up in
https://gitlab.com/gitlab-org/omnibus-gitlab/issues/4126.

For the sake of consistency, removes any extraneous
consecutive blank lines from the doc suite.

`queue_duration` is a useful metric that is currently in api_json.log
but not in production_json.log. We should add it because it tells us how
long the request sat in Workhorse before Unicorn processed it. Having
this field enables the support team to better troubleshoot when delays
began to happen.

Instead of requiring one separate document for every version (which is
created by release managers), we now use a single document for both
Community Edition and Enterprise Edition. This allows developers to add
guidelines right away, instead of release managers having to determine
what to add.

Version specific upgrading instructions are placed in a separate
section. This prevents instructions from lingering around for many
versions should a developer forget to remove them. This also ensures
that all instructions are kept in a single place, instead of being
spread across different documents.

A minor downside is that CE and EE guidelines now live in the same
document, which could cause merge conflicts. Since we are working
towards a single codebase, this should only be an issue until we merge
the codebases together; something we expect to do in the coming months.

This commit also removes all old upgrading instructions, but these can
still be accessed using Git branch specific URLs (included in the
updating README).

Cached markdown version is composed both from global and local
markdown version. This allows admins to bump version locally when
needed (e.g. when external URL is changed).

Update the list of GitLab metrics to include the missing metric names.