Clusters::Applications models removal

Why

Part of Remove clusters_applications_* code (#366573 - closed)

What

This issue will track and provide a point of conversation for the related Clusters::Applications models that are going to be removed.

Begin by looking into each of the models defined in app/models/clusters/applications

Merge requests

• cert_manager.rb MR
• cilium.rb
• crossplane.rb
• helm.rb (merge last)
• ingress.rb
• jupyter.rb
• knative.rb
  • serverless cluster domain see: !113268 (comment 1299506346)
• prometheus.rb
• runner.rb

It will be safest and easiest to review if we remove these in individual merge requests.

Next steps

For each model that gets removed, we'll want to remove the database tables and documentation as well.

table_name: serverless_domain_cluster will also need to be included in the table removal.

Issue to track it db table removal: Remove Clusters::Application database tables (#397760 - closed)