Implement remaining parts for the Helm-direct plugin

[antgamdia]

As #3085 and #3165 became really big issues (we tracked the status there), I'm opening this new one just to track the remaining or unfinished aspects preventing us from having a fully-working Helm-direct plugin.

• [kubeapps-apis] Agreement for methods and messages for packaging API in design doc. #2944
  • Proposal for DeleteInstalledPackage messages. #3427
  • Add helm-only implementation of RollbackInstalledPackage. #3487
• Implement already agreed operations (Helm plugin)
  • Kubeapps-APIs implementation of helm create installed pkg  #3371
  • Add UpdateInstalledPackage for Helm plugin. #3430
  • Implement delete installed package. #3459
  • Add helm-only implementation of RollbackInstalledPackage. #3487
• Use core APIs instead of the Helm ones
  • Initial implementation of the remaining core apis operations #3376
  • Use the core apis in the UI #3377
• Use new core API instead of Kubeops for managing Helm:
  • Add initial createInstalledPkg from UI #3463
  • Add initial updateInstalledPkg from UI #3476
  • Add initial deleteInstalledPkg from UI  #3475
  • Add initial rollbackInstalledPkg from UI  #3490
• Bug-hunting:
  • Don't cache clients that are created (without auth) when app loads. #3338
  • Unable to use Kubeapps under a subpath #3368
  • Ensure relative path is used for kubeappsapis so any subpath is included. #3369
• On-the-fly refactoring:
  • Add plugin-specific user-agent to kubeapps-apis helm plugin #3373
  • Refactor the helm and OCI chart clients and respective fakes. #3370
  • Update chart.RegistrySecretsPerDomain to depend on kube clientset only. #3362
  • Add plugin version to the UI paths #3439
• Remove old references to charts in the UI code #3533

Feel free to edit this issue to add something I might have missed.

Updated on September 30th

[absoludity]

  * [ ]  Continue checking the issue in [Don't cache clients that are created (without auth) when app loads. #3338](https://github.com/kubeapps/kubeapps/pull/3338)
    
    * [ ]  Perhaps related to: `Response closed without grpc-status (Headers only)` in `GetInstaledPackageSummaries`

The problem that was addressed by #3338 was completely reproducible in a local environment when using token authentication, and is easy to demonstrate the fix in that PR fixing it. Not sure why you think that particular problem still needs investigating, or why it would be related to the Response closed without grpc-status issue?

Also, perhaps this issue could be merged with #3146.

[antgamdia]

The problem that was addressed by #3338 was completely reproducible in a local environment when using token authentication, and is easy to demonstrate the fix in that PR fixing it. Not sure why you think that particular problem still needs investigating, or why it would be related to the Response closed without grpc-status issue?

Yes, not related at all. I just added that message during the release process, so that we don't forget about it. Edited now.

Also, perhaps this issue could be merged with #3146.

Yes... we have so many open ongoing issues that sometimes we just duplicate some content. Let's see if we can organize them better for the next iteration.

[antgamdia]

Closing (FINALLY!!) as all the related PRs have already been merged 🎉