✨ Bring your own network

[johannesfrey]

What this PR does / why we need it: This PR makes it possible to "adopt" a pre-existing network by passing its ID to hetznerCluster.spec.hcloudNetwork.id instead of the network being created during cluster creation. Furthermore, during cluster deletion it only deletes the attached network if it does not have the owned label attached to it (currently the only way here to discriminate between a CAPH-managed network and an unmanaged one).

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): Fixes #762

Special notes for your reviewer: This has been lingering around for a while untouched on my fork and I decided to rebase it onto the current main branch. Please consider this as a first attempt to approach this topic as a whole. I also tried to already add some unit tests. I guess it also might require some e2e tests!? No idea if this is the desired way to do this and about other side-effects I did not see. So looking forward for feedback or any pointers. And also feel free to push changes to the PR, as I'll be pretty occupied with other things almost the whole September. Just wanted to push this out there already for you to take a look at 🙂

The most controversial changes so far:

• Making hcloudNetwork.id mutually exclusive with cidrBlock, subnetCidrBlock and networkZone
• Replacing kubebuilder defaulting/validation special tags with custom defaulting/validation, which makes the webhook more complex
• Changing cidrBlock, subnetCidrBlock and networkZone to be pointers (I guess this could also be done with empty strings, but pointers make it possible to be not shown at all, when not provided)
• Labels are shown in the NetworkStatus in order to check if it's managed or unmanaged

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• [ ] squash commits
• [ ] include documentation
• [x] add unit tests

[johannesfrey]

Thanks a lot again for this PR @johannesfrey. I think we can merge it if you follow the suggestions I gave. It's really good work!

Sorry for the long delay 🙏 . Thx for the reviews! I hope I addressed your suggestions correctly. PTAL. Thx!