WIP: Backend: Add Sentry as a GitLab managed app

What does this MR do?

This is an initial MR to get Sentry deployed as a GitLab managed app.

What is included

• Migrations to set up the Sentry cluster application
• Filled out a minimal configuration in order for the Sentry app to be deployed and the user able to log into the Web UI.
• Can be manually deployed with Clusters::Applications::InstallService.new(sentry_app).execute

What will come in subsequent MRs

• frontend implementation
• Ability to configure more settings, such an SMTP email settings.
• GitLab Managed Apps V2 config (&2103)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Testing

To test you can do the following

1. Connect a Cluster to your GitLab project: https://docs.gitlab.com/ee/user/project/clusters/add_remove_clusters.html#add-existing-gke-cluster
2. Install ingress
3. Manually setup Sentry application: Clusters::Applications::Sentry.create!(cluster: <cluster>, hostname: 'sentry.<ingress-ip>')
4. Set the application to 'installable': sentry.update(status: 1)
5. Install Sentry Clusters::Applications::InstallService.new(sentry).execute

Relates to #26513 (closed)