Remove Settingslogic gem

- For better backward compatibility use string keys on
  GitlabSettings::Options
- Remove all the Settingslogic references from code (not comments)
- Ensure to use GitlabSettings::Options when pushing new options to
  Array values
- Instead of inheriting from Hash, wrap a hash in
  GitlabSettings::Options and make it respond to all the requirements.
    * PROS: This provides more autonomy on what needs to be done
    * CONS: Some places were checking by Hash, we need to tackle these
    scenarios
- Ensure to deep_merge return nested Options
- Use the _raw_ version of options when passing to Fog::Storage
- Ensure to load required active_support libraries
- Show the option name in the GitlabSettings::MissingSetting error
- Ensure to have an option `source` for the path of the `gitlab.yml`
- Fix GitlabSettings::Options#deep_merge and
  GitlabSettings::Options#merge to return a new GitlabSettings::Options
  object with the options deep_merged/merged
- Add GitlabSettings#reload! for backward compatibility
- Make file/namespace initializer arguments
- Avoid mutating Settings in sidekiq_cluster/cli tests
- Fix configuration stubbing

Related to: https://gitlab.com/gitlab-org/gitlab/-/issues/286873