✨ POC for mounts (Master PR, not for merging)

[mjudeikis]

Summary

This PR is a working example of workspace mounts mounting remote cluster on top of it.

• In general everything in contrib directory in the long term will go to the separate repository (We can keep it here if people agree too).
• Any code in core would need to be split and merged as smaller prs.

In addition this enables core to run with bit more flexible mini-front-proxy, as I found very hard to develop external VirtualWorskapces using kcp start so kinda took it and extended.

This add example of following:

mjudeikis@unknown2:/go/src/github.com/kcp-dev/kcp/contrib/mounts-vw$ k ws tree
.
└── root
    ├── consumer
    │   └── kind-cluster
    ├── operators
    │   └── mounts
    └── providers
        └── mounts

where:
root:providers:mounts is where all APIExports lives and where code operators are looking at.
root:operators:mounts is where people operators created their bindings and created TARGET cluster objects (separate binding)
root:consumers where consumer bounded MOUNT apiexport and created a single mount ws kind-cluster with mount backed by Target API.

In addition when bootstrapping shard-aware operators - it's painful and hard to make miskates. I did some skeleton but I think we need a framework for this.

In general this this WIP PR, to be split to many many smalls ones.

✔️ #3188 Fix regression when generating deep copy
✔️ #3183 Add workspace phase update logic
🖊️ #3199 enable dev mode

Related issue(s)

#3189 as follow-up

Release Notes

NONE

[kcp-ci-bot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[kcp-ci-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please ask for approval from mjudeikis. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS
• config/crds/OWNERS
• sdk/apis/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[kcp-ci-bot]

PR needs rebase.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.