Made google_container_cluster.user_managed_keys_config not settable and fixed diff due to server-set values

[melinath]

Fixes hashicorp/terraform-provider-google#20301

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container: fixed diff on `google_container_cluster.user_managed_keys_config` field for resources that had not set it. (patch release)

container: marked `google_container_cluster.user_managed_keys_config` as immutable because it can't be updated in place. (patch release)

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 2 files changed, 173 insertions(+), 14 deletions(-))
google-beta provider: Diff ( 2 files changed, 172 insertions(+), 14 deletions(-))

[modular-magician]

Tests analytics

Total tests: 214
Passed tests: 201
Skipped tests: 12
Affected tests: 1

Click here to see the affected service packages

• container

Action taken

Found 1 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

• TestAccContainerCluster_withFleetConfig

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[modular-magician]

🔴 Tests failed during RECORDING mode:
TestAccContainerCluster_withFleetConfig [Error message] [Debug log]

🔴 Errors occurred during RECORDING mode. Please fix them to complete your PR.

View the build log or the debug log for each test

[melinath]

Failure looks unrelated. GA test run: https://hashicorp.teamcity.com/buildConfiguration/TerraformProviders_GoogleCloud_GOOGLE_MMUPSTREAMTESTS_GOOGLE_PACKAGE_CONTAINER/265034?hideTestsFromDependencies=false&hideProblemsFromDependencies=false

[melinath]

New GA test run - first one I picked an alternate test that's consistently failing: https://hashicorp.teamcity.com/buildConfiguration/TerraformProviders_GoogleCloud_GOOGLE_MMUPSTREAMTESTS_GOOGLE_PACKAGE_CONTAINER/265038?hideProblemsFromDependencies=false&hideTestsFromDependencies=false