Introduce simplified Default credential provision

As the first step in credential consolidation, we replace
injection of application default credential in for KMS and
Drive.

Tests:
- for Drive, tested with exportDomainLists and exportReservedTerms.
- For KMS, used CLI commands (get_keyring_secret and update_kms_keyring) to change and
  restore secret for one key.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=211819859

java/google/registry/module/backend/BackendComponent.java

@@ -18,6 +18,7 @@ import com.google.monitoring.metrics.MetricReporter;
 import dagger.Component;
 import dagger.Lazy;
 import google.registry.bigquery.BigqueryModule;
+import google.registry.config.CredentialModule;
 import google.registry.config.RegistryConfig.ConfigModule;
 import google.registry.export.DriveModule;
 import google.registry.export.sheet.SheetsServiceModule;
@@ -55,6 +56,7 @@ import javax.inject.Singleton;
       BackendRequestComponentModule.class,
       BigqueryModule.class,
       ConfigModule.class,
+      CredentialModule.class,
       DatastoreServiceModule.class,
       DirectoryModule.class,
       google.registry.keyring.api.DummyKeyringModule.class,