Enforced immutable fields using CEL rules

[NeerajNagure]

Description of your changes

Added CEL based comment markers to enforce immutability on every field that was previously marked as // +immutable

Fixes #4128

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable to ensure this PR is ready for review.
• Added or updated unit tests.
• Added or updated e2e tests.
• Linked a PR or a docs tracking issue to document this change.
• Added backport release-x.y labels to auto-backport this PR.

Need help with this checklist? See the cheat sheet.

[negz]

Did you run make generate? It doesn't seem like the CRDs were updated with the result of the new comment marker.

Also, I'm pretty confident we have more immutable fields than this. There's probably some without // +immutable markers.

[NeerajNagure]

@negz Also can I please know how can I find those fields that are supposed to be immutable but are not marked with //+immutable ?

[negz]

Also can I please know how can I find those fields that are supposed to be immutable but are not marked with //+immutable ?

@NeerajNagure Unfortunately there's no easy way to do this. You'd need to be familiar enough with Crossplane's APIs to know which fields can't change. I don't think this needs to block this PR though, if we can come up with a pattern that works someone who is familiar with the APIs can copy it to the other fields that need it.

[NeerajNagure]

@negz can you please review this?

[NeerajNagure]

@negz I have made the changes as suggested by you

[negz]

Thanks @NeerajNagure. Could you please add some details on how you've tested this change? Adding an E2E test would be ideal.

[NeerajNagure]

@negz I have added 2 e2e tests that check if its possible to update immutable fields or not (Also those e2e tests pass successfully)