Allow updating single_cluster_routing in google_bigtable_app_profile

[rileykarson]

Fixes b/168053560 (updating certain bt app profile fields failed)

Terraform believed the subfields of single_cluster_routing were updatable and they should have been, but in practice Magic Modules didn't generate the write update handlers.

I don't believe updating to/from single_cluster_routing and multi_cluster_routing is possible, so this schema is a little misleading. However I believe it's an acceptable tradeoff:

• Since this and mcr are ExactlyOneOf, mcr's ForceNew will still trigger if the user changes which field is set
• MM doesn't support updating fields that are updatable while their parent field isn't
• MM doesn't support update masks for non-top-level fields (but specifying the top level field will update all of it's children)

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)

bigtable: fixed the update behaviour of the `single_cluster_routing` sub-fields in `google_bigtable_app_profile`

[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, 22 insertions(+), 5 deletions(-))
Terraform Beta: Diff ( 2 files changed, 22 insertions(+), 5 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=145604"

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccComposerEnvironment_update|TestAccComposerEnvironment_withDatabaseConfig|TestAccComposerEnvironment_withWebServerConfig|TestAccComputeSnapshot_encryptionCMEK You can view the result here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=145613"

[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, 26 insertions(+), 9 deletions(-))
Terraform Beta: Diff ( 2 files changed, 26 insertions(+), 9 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=145622"

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccComposerEnvironment_update|TestAccComposerEnvironment_withDatabaseConfig|TestAccComposerEnvironment_withWebServerConfig|TestAccComputeSnapshot_encryptionCMEK|TestAccComputeUrlMap_trafficDirectorPathUpdate|TestAccComputeUrlMap_trafficDirectorRemoveRouteRule|TestAccComputeUrlMap_defaultUrlRedirect|TestAccDataCatalogTagTemplate_dataCatalogTagTemplateBasicExample|TestAccDataCatalogTag_dataCatalogEntryTagBasicExample|TestAccDataCatalogTag_dataCatalogEntryGroupTagExample|TestAccDataLossPreventionInspectTemplate_dlpInspectTemplateBasicExample|TestAccDataCatalogTag_dataCatalogEntryTagFalseExample|TestAccDataLossPreventionInspectTemplate_dlpInspectTemplateUpdate|TestAccDataCatalogTag_update|TestAccDialogflowIntent_dialogflowIntentFullExample|TestAccDialogflowIntent_update|TestAccDialogflowEntityType_update|TestAccHealthcareFhirStore_healthcareFhirStoreBasicExample|TestAccHealthcareFhirStore_healthcareFhirStoreStreamingConfigExample|TestAccHealthcareFhirStore_basic|TestAccHealthcareHl7V2Store_healthcareHl7V2StoreParserConfigExample|TestAccIdentityPlatformInboundSamlConfig_inboundSamlConfigUpdate|TestAccIdentityPlatformDefaultSupportedIdpConfig_defaultSupportedIdpConfigUpdate|TestAccIdentityPlatformOauthIdpConfig_identityPlatformOauthIdpConfigUpdate|TestAccIdentityPlatformTenantDefaultSupportedIdpConfig_identityPlatformTenantDefaultSupportedIdpConfigUpdate|TestAccIdentityPlatformTenantInboundSamlConfig_identityPlatformTenantInboundSamlConfigUpdate|TestAccIdentityPlatformTenantOauthIdpConfig_identityPlatformTenantOauthIdpConfigUpdate|TestAccIdentityPlatformTenant_identityPlatformTenantUpdate|TestAccMonitoringGroup_update|TestAccMonitoringUptimeCheckConfig_uptimeCheckConfigHttpExample|TestAccMonitoringUptimeCheckConfig_uptimeCheckConfigHttpsExample|TestAccMonitoringUptimeCheckConfig_update|TestAccMonitoringUptimeCheckConfig_changeNonUpdatableFields|TestAccOSConfigPatchDeployment_osConfigPatchDeploymentFullExample|TestAccOSConfigGuestPolicies_osConfigGuestPoliciesRecipesExample|TestAccOSConfigPatchDeployment_osConfigPatchDeploymentInstanceExample|TestAccPubsubSubscription_pubsubSubscriptionPullExample|TestAccPubsubSubscription_emptyTTL|TestAccPubsubSubscription_update You can view the result here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=145623"

[megan07]

LGTM!