Review and adapt existing Kubeapps documentation to comply with new guidelines

[castelblanque]

Summary Review and adapt existing Kubeapps documentation to comply with new guidelines defined in #5019.

Background and rationale New guidelines for documentation have been added to Kubeapps in #5019 and PR #5020. This newly required way of writing may differ from the existing documentation.

Description This tasks consists in adapting/rewriting existing Kubeapps documentation to the new standard, for example: from Under the hood, kapp-controller will create... in this document about Carvel packages, to Internally, ``kapp-controller`` will create....

Acceptance criteria Documentation is rewritten meeting the new guidelines, where needed.

[ppbaena]

Summary:

• [X] General documentation
• [x] Tutorials
• [ ] How-to guides
  • [ ] Update How-to guides related to Forms after the revamping
  • [ ] Update How-to guide for Custom App View
  • [ ] Update how-to guide for multi-cluster support
• [ ] Background
  • [ ] Define architecture diagram of Kubeapps as code
• [ ] Reference
  • [ ] Update developer guides

[ppbaena]

Working on How-to guides:

• [x] Access Control
• [x] Dashboard
• [x] Offline Installation
• [x] Private Package Repository
• [x] Using an OIDC provider with Pinniped

The rest of the How-to guides will be updated on specific issues as the team is currently working on issues related to them.

[ppbaena]

I've created specific issues for updating pending documentation to be updated and aligned to work in progress in different components (forms, multi-cluster, architecture, etc.).