The Metrics Dashboard (used for monitoring apps deploying using gitlab)
was deprecated in 14.7 and removed from the product in 16.0.
This commit cleans up a portion of the dead code.

https://gitlab.com/groups/gitlab-org/-/epics/10107

Remove product_stage leftovers

Add new rails generator that creates configuration files for
gitlab internal events tracking feature.

Changelog: other

Match YAML files with any ending and exclude extension which are known
to break yamllint. For example, *.erb, *.gz, *.bz2.

The following files are checked additionally:
- ./config/secrets.yml.example
- ./config/database.yml.postgresql
- ./config/resque.yml.example
- ./config/cable.yml.example
- ./config/gitlab.yml.example
- ./config/database.yml.decomposed-postgresql
- ./config/sidekiq.yml.example
- ./.solargraph.yml.example

Enforce braces to be used with a single space inside. Empty braces don't
have a space:

  good: { this_is: ok }
  empty: {} #  Also OK

  bad: {this_is: too_little}
  also_bad: {  this_is: too_much  }
  empty: { } #  # Also bad

This commit adds CI job that validates all `*.yml`
with `yamllint`.

This commit fixes all offenses present in repository.

This commit adds CI job that validates all `*.yml`
with `yamllint`.

This commit fixes all offenses present in repository.