docs: samples and tests for database Admin APIs.

[arpan14]

Adds samples and tests for auto-generated Database Admin APIs.

[snippet-bot]

Here is the summary of changes.

You are about to add 22 region tags.

• samples/snippets/src/main/java/com/example/spanner/admin/generated/AddAndDropDatabaseRole.java:19, tag spanner_add_and_drop_database_role
• samples/snippets/src/main/java/com/example/spanner/admin/generated/AddJsonColumnSample.java:19, tag spanner_add_json_column
• samples/snippets/src/main/java/com/example/spanner/admin/generated/AddJsonbColumnSample.java:19, tag spanner_postgresql_jsonb_add_column
• samples/snippets/src/main/java/com/example/spanner/admin/generated/AddNumericColumnSample.java:19, tag spanner_add_numeric_column
• samples/snippets/src/main/java/com/example/spanner/admin/generated/AlterSequenceSample.java:19, tag spanner_alter_sequence
• samples/snippets/src/main/java/com/example/spanner/admin/generated/AlterTableWithForeignKeyDeleteCascadeSample.java:19, tag spanner_alter_table_with_foreign_key_delete_cascade
• samples/snippets/src/main/java/com/example/spanner/admin/generated/CreateDatabaseWithVersionRetentionPeriodSample.java:19, tag spanner_create_database_with_version_retention_period
• samples/snippets/src/main/java/com/example/spanner/admin/generated/CreateSequenceSample.java:19, tag spanner_create_sequence
• samples/snippets/src/main/java/com/example/spanner/admin/generated/CreateTableWithForeignKeyDeleteCascadeSample.java:19, tag spanner_create_table_with_foreign_key_delete_cascade
• samples/snippets/src/main/java/com/example/spanner/admin/generated/DropForeignKeyConstraintDeleteCascadeSample.java:19, tag spanner_drop_foreign_key_constraint_delete_cascade
• samples/snippets/src/main/java/com/example/spanner/admin/generated/DropSequenceSample.java:19, tag spanner_drop_sequence
• samples/snippets/src/main/java/com/example/spanner/admin/generated/EnableFineGrainedAccess.java:19, tag spanner_enable_fine_grained_access
• samples/snippets/src/main/java/com/example/spanner/admin/generated/GetDatabaseDdlSample.java:19, tag spanner_get_database_ddl
• samples/snippets/src/main/java/com/example/spanner/admin/generated/ListDatabaseRoles.java:19, tag spanner_list_database_roles
• samples/snippets/src/main/java/com/example/spanner/admin/generated/ListDatabasesSample.java:19, tag spanner_list_databases
• samples/snippets/src/main/java/com/example/spanner/admin/generated/PgAlterSequenceSample.java:19, tag spanner_postgresql_alter_sequence
• samples/snippets/src/main/java/com/example/spanner/admin/generated/PgCaseSensitivitySample.java:19, tag spanner_postgresql_identifier_case_sensitivity
• samples/snippets/src/main/java/com/example/spanner/admin/generated/PgCreateSequenceSample.java:19, tag spanner_postgresql_create_sequence
• samples/snippets/src/main/java/com/example/spanner/admin/generated/PgDropSequenceSample.java:19, tag spanner_postgresql_drop_sequence
• samples/snippets/src/main/java/com/example/spanner/admin/generated/PgInterleavedTableSample.java:19, tag spanner_postgresql_interleaved_table
• samples/snippets/src/main/java/com/example/spanner/admin/generated/UpdateDatabaseSample.java:19, tag spanner_update_database
• samples/snippets/src/main/java/com/example/spanner/admin/generated/UpdateDatabaseWithDefaultLeaderSample.java:19, tag spanner_update_database_with_default_leader

You are about to delete 1 region tag.

• samples/snippets/src/main/java/com/example/spanner/admin/generated/CreateDatabaseWithDefaultLeaderSample.java:19, tag spanner_create_database_with_default_leader

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[generated-files-bot]

Warning: This pull request is touching the following templated files:

• samples/pom.xml