Database::MonitorLockedTablesWorker to address all self-managed

Context: #480643 (comment 2074662654)

Database::MonitorLockedTablesWorker is responsible for monitoring tables that are supposed to be locked, but haven't been locked for some reason. See here: https://docs.gitlab.com/ee/development/database/multiple_databases.html#monitoring.

The Monitoring job also locks those tables, but that's controlled via an ops feature flag, which is enabled for GitLab.com already, but not enabled by default for self-managed.

Requirements (probably via 1 MR Only)

• This con job is only enabled for ee. But we should enable it for ce as well: https://gitlab.com/gitlab-org/gitlab/-/blob/master/config/initializers/1_settings.rb#L757
• Keep the Feature Flag, but enable it by default for self-managed. By modifying the YAML file of the feature flag, default_enabled: true

References

• https://docs.gitlab.com/ee/development/feature_flags/
• https://docs.gitlab.com/ee/development/database/multiple_databases.html#monitoring