Promote release_channel_default_version field in data.google_container_engine_versions to GA

[rileykarson]

One last failing test after #3837 uses this field.

Release Note Template for Downstream PRs (will be copied)

container: added `release_channel_default_version` field to `data.google_container_engine_versions` (GA) 

[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, 12 insertions(+), 1 deletion(-))
Terraform Beta: Diff ( 2 files changed, 1 insertion(+), 2 deletions(-))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=138147"

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccCloudBuildTrigger_cloudbuildTriggerBuildExample|TestAccCloudBuildTrigger_basic|TestAccComputeInstanceTemplate_shieldedVmConfig1|TestAccComputeInstanceTemplate_shieldedVmConfig2|TestAccComputeInstance_shieldedVmConfig1|TestAccComputeInstance_shieldedVmConfig2|TestAccContainerCluster_misc|TestAccContainerCluster_withReleaseChannelEnabled|TestAccContainerCluster_withInvalidReleaseChannel|TestAccContainerCluster_withReleaseChannelEnabledDefaultVersion|TestAccEndpointsService_basic|TestAccFolderIamAuditConfig_multiple|TestAccOSConfigPatchDeployment_osConfigPatchDeploymentFullExample|TestAccRedisInstance_redisInstancePrivateServiceExample|TestAccRedisInstance_redisInstanceFullExample|TestAccSqlDatabaseInstance_dontDeleteDefaultUserOnReplica|TestAccSqlDatabaseInstance_settings_basic|TestAccSqlDatabaseInstance_replica|TestAccSqlDatabaseInstance_slave|TestAccSqlDatabaseInstance_highAvailability|TestAccSqlDatabaseInstance_settingsDowngrade|TestAccSqlDatabaseInstance_PointInTimeRecoveryEnabled|TestAccSqlDatabaseInstance_settings_upgrade|TestAccSqlDatabaseInstance_authNets|TestAccSqlDatabaseInstance_basic_with_user_labels You can view the result here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=138149"