📖 Refactor documentation sections and mention Helm chart

[embik]

Summary

This PR takes a stab at reworking the structure of our documentation to clearly split topic and help people find the right information depending on their own context.

The following top-level sections exist now:

• Home - landing page and goals, extracted the quickstart out of this.
• Setup - this is new and gathers all the various ways and tools for kcp setups. The quickstart and kubectl plugin setup has been moved here, but a short page referencing the Helm chart has also been added.
• Concepts - this mostly stayed the same in purpose, but subsections have been added to give the whole section more structure.

• Developers - this section now mostly targets developers that want to develop against kcp, e.g. writing their own controllers.
• Contributing - new section that holds the existing "CONTRIBUTING.md" content and also gathers everything related to developing (i.e. contributing to) kcp.
• Reference - no changes here except for some index pages.

Overall, I've mostly shifted around content (sometimes whole files, sometimes parts of a longer document) to accommodate the new structure. Here and there I've also updated content (e.g. the quickstart doesn't need a kind cluster; this was probably a leftover from trying out TMC with it).

Related issue(s)

Fixes #

Release Notes

NONE

[embik]

/cc @xrstf @sttts @mjudeikis

[mjudeikis]

/lgtm
/approve
/hold

[kcp-ci-bot]

LGTM label has been added.

Git tree hash: a11e307a7093334ea50c4e4a2f76e768f9e38370

[kcp-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mjudeikis

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[mjudeikis]

I think we can iterate ontop if something is off

[embik]

I think we can iterate ontop if something is off

That's the idea. It deploys to https://docs.kcp.io/kcp/main anyway, not to the "stable" docs. Who/when would you like to lift the hold? After a second review?

[xrstf]

/hold cancel