Add comments to skipped sweepers (#10028)

Author: hao-nan-li

mmv1/products/secretmanager/SecretVersion.yaml

@@ -20,6 +20,7 @@ delete_url: '{{name}}:destroy'
 delete_verb: :POST
 description: |
   A secret version resource.
+# Sweeper skipped as this resource has customized deletion.
 skip_sweeper: true
 examples:
   - !ruby/object:Provider::Terraform::Examples

mmv1/products/spanner/Database.yaml

@@ -41,6 +41,7 @@ async: !ruby/object:Api::OpAsync
     path: 'error'
     message: 'message'
 autogen_async: true
+# Sweeper skipped as this resource has customized deletion.
 skip_sweeper: true
 id_format: '{{instance}}/{{name}}'
 import_format:

mmv1/products/sql/Database.yaml

@@ -30,6 +30,7 @@ import_format:
     '{{instance}}/{{name}}',
     '{{name}}',
   ]
+# Sweeper skipped as this resource has customized deletion.
 skip_sweeper: true
 examples:
   - !ruby/object:Provider::Terraform::Examples