Improve the UX of new Repositories API in the UI

[antgamdia]

Once the new Repos API is being used in the UI (#4764), there are several improvements and pending items to be performed.

This issue is intended to hold and sum up those pending items/open issues, so that we can track the overall status easily:

Phase 2

• Issues already solved with the new UI

  • See status of AppRepository syncs (especially failures) in UI #153
  • Global repositories handling is inconsistent - Carvel issue #5200

• Issues to solve in a timely manner:

  • Minor UI tweak if Flux were to support OCI
    • Tracked at: Support for OCI registries in Flux plugin #5007
  • Carvel repositories are not visible in Helm global namespace #5201
  • Improve docs adding info about the repos
    • Tracked at: Update the carvel+flux docs explaining how to add repos with the UI #5220
  • Ensure the proper usage of the global namespace, move to isGlobalNamespace(... function when possible.
  • Tracked at: Refactor/Rewrite frontend handling of global namespaces across plugins #5202
  • getPluginByName is a hardcoded list of plugin objects for getting the object with the version set. Ideally, it should fetch it from the actually configured plugins.
    • Tracked at: Make getPluginByName be plugin-aware #5017
  • (blocked by the backend) Ensure the UI works as expected after stopping using config-level flags
    • Example: [Repository] refactor helm to use managed-by annotation instead of system flag #4870

• Not critical issues (rbac/multicluster) as of today:

  • (multicluster) Inconsistent message if viewing app repositories on non-kubeapps cluster #2717
  • (rbac) UI error flashes when trying to delete a repository without permissions #4220
  • (rbac) App Repository UI does not properly handle cases where the user does not have read/write to app repos in ns #3679
  • (rbac) Listing all repositories an unpriviledged users can access to #5215

Further improvements will be tracked by issue #5515