feat(xrd): Add support for version deprecation

[MisterMX]

Description of your changes

This adds two new fields deprecated and deprecationWarning to XRDs spec.versions[] that match their CRD counterparts.

Fixes #2945

I have:

• Read and followed Crossplane's [contribution process].
• Run make reviewable to ensure this PR is ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

How has this code been tested

Manually

[hasheddan]

LGTM -- I'm a fan of this change even though in practice I believe we can still only offer one XRD version at a time. Would like to get @negz thoughts before merge.

[hasheddan]

Are these comments wrapped at 80 characters? If not could you make sure to wrap them! 🙂

[MisterMX]

Fixed

[MisterMX]

@hasheddan thanks for the review! I fixed the line lengths. Let me know if something is missing.

Regarding serving multiple XRD versions: AFAIK Crossplane does support multiple versions at the same time.

However, our main use case is to let users know when they use a deprecated version. In some cases we do deprecate complete XRDs so we might need this for every version.

[negz]

AFAIK Crossplane does support multiple versions at the same time.

Kind of. It supports it as long as all the versions are identical. :) So, that said, this feature makes sense. e.g.:

1. You start with a v1alpha1 API.
2. You 'promote' the API by introducing an identical v1beta1 variant.
3. You mark the v1alpha1 API deprecated.

Eventually we'll support introducing new API versions with different schemas per #2608.