Add support for cacheKeyPolicy in BackendBuckets

[modular-magician]

This PR adds support for cacheKeyPolicy in google_compute_backend_bucket.

Resolves #11114.

This is my first PR to this repo so feel free to correct me if there is anything wrong.

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)

compute: added `cache_key_policy` field to `google_compute_backend_bucket` resource

Question:
After I ran make terraform, make lint fails because of the files that seem to be irrelevant to my changes. Is this an expected behavior?

output of `make lint` (hashicorp-provider-google)

$ cd /path/to/hashicorp/terraform-provider-google
$ git log -n 1 | head -n 1
commit 05616d2ee0e1e676ff042fc96187d20dcb51d9ab
$ golangci-lint --version
golangci-lint has version 1.46.2 built from a333689 on 2022-05-17T06:05:08Z
$ make lint
==> Checking source code against linters...
google/config_test.go:67:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/config_test.go:95:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/config_test.go:125:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/config_test.go:165:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/resource_compute_disk_test.go:188:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/resource_compute_instance_migrate_test.go:21:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/resource_compute_instance_migrate_test.go:125:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/resource_compute_instance_migrate_test.go:153:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/resource_compute_instance_migrate_test.go:221:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/resource_compute_instance_migrate_test.go:288:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/resource_compute_instance_migrate_test.go:369:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/resource_compute_instance_migrate_test.go:449:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/resource_compute_instance_migrate_test.go:518:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/resource_compute_instance_migrate_test.go:586:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/resource_compute_instance_migrate_test.go:659:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/resource_compute_instance_migrate_test.go:731:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
google/resource_compute_instance_migrate_test.go:797:3: S1038: should use t.Skipf(...) instead of t.Skip(fmt.Sprintf(...)) (gosimple)
		t.Skip(fmt.Sprintf("Network access not allowed; use %s=1 to enable", TestEnvVar))
		^
make: *** [lint] Error 1

Derived from GoogleCloudPlatform/magic-modules#6043

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