[resource_container_cluster] - Add self-link property

[ScottSuarez]

Add self link property to resource_container_cluster.

Resolves 7120

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

container: Added `self_link` to google_container_cluster

[modular-magician]

Hello! I am a robot who works on Magic Modules PRs.

I have detected that you are a community contributor, so your PR will be assigned to someone with a commit-bit on this repo for initial review.

Thanks for your contribution! A human will be with you soon.

@megan07, please review this PR or find an appropriate assignee.

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 1 file changed, 75 insertions(+), 60 deletions(-))
Terraform Beta: Diff ( 1 file changed, 101 insertions(+), 89 deletions(-))

[megan07]

Hi @ScottSuarez! Were you able to build this locally? If you need any help with that, feel free to reach out!

[megan07]

I think we want a comma after this here.

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 1 file changed, 7 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 1 file changed, 7 insertions(+), 2 deletions(-))

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 2 files changed, 13 insertions(+), 6 deletions(-))
Terraform Beta: Diff ( 2 files changed, 13 insertions(+), 6 deletions(-))

[megan07]

Looks good! Thanks for cleaning up the whitespace. Do you think we should add a test in for this?

[ScottSuarez]

Looks good! Thanks for cleaning up the whitespace. Do you think we should add a test in for this?

It certainly couldn't hurt! I added the property validation to an existing basic test and ran it locally.

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 3 files changed, 15 insertions(+), 7 deletions(-))
Terraform Beta: Diff ( 3 files changed, 15 insertions(+), 7 deletions(-))