GitLab

This applies to EE queries only. It improves performance of those
queries significantly.

Related to https://gitlab.com/gitlab-org/gitlab-exporter/issues/58

gitlab-monitor is now called gitlab-exporter.

Retreive Sidekiq stats metrics from
https://github.com/mperham/sidekiq/blob/v5.2.7/lib/sidekiq/api.rb#L106Signed-off-by: chiehminw <chiehminw@synology.com>

Related to https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5313

We provide sensible defaults for the `server` section for all cases.
However, if the `server` part is totally absent from the config file,
this fails to provide a default for `memory_threshold`.

The queries are largely based on work from
https://github.com/ioguix/pgsql-bloat-estimation.

Context:
https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/6178

This adds an optional `redis_enable_client` config option that will turn
off the CLIENT command when talking to the Sidekiq API.

Relates to https://gitlab.com/gitlab-org/omnibus-gitlab/issues/4164

When launched via Ruby, `pgrep` is launched via a shell (e.g. `sh -c
pgrep foo bar`). When the `-f` flag is used with pgrep with a regex that
has multiple words, it appears that that the shell is always matched.

We can work around this issue by getting back the process name and
filtering out `sh` from the list.

Closes https://gitlab.com/gitlab-org/gitlab-monitor/issues/44

* Simplify use by reading all stats from `/proc/<pid>/stat`.
* Simplify metrics for total resident and virtual bytes.
* Use process start time to fit with Prometheus conventions.
* Add process CPU seconds metric.

Add a boolean metric for the `paused?`[0] state of each queue.

[0]: https://www.rubydoc.info/github/mperham/sidekiq/Sidekiq/Queue

* Fix consistency of `_jobs` as the "type".
* Remove extraneous `_count` and `_total` on gauges.
* Update README.

Avoid conflict with postgres_exporter `pg_`.

As mentioned in https://gitlab.com/gitlab-org/omnibus-gitlab/issues/3772#note_99878357,
the version number was not updated.

Only run pull mirror related queries when `plans` table exists, which means we're running against EE