chore(samples): add cloud-retail-team as sample owners (#137)

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
- [ ] Make sure to open an issue as a [bug/issue](https://github.com/googleapis/nodejs-retail/issues/new/choose) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
- [ ] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)

packages/google-cloud-retail/.repo-metadata.json

@@ -12,5 +12,6 @@
   "name": "retail",
   "issue_tracker": "https://github.com/googleapis/nodejs-retail/issues",
   "api_shortname": "retail",
-  "library_type": "GAPIC_AUTO"
+  "library_type": "GAPIC_AUTO",
+  "codeowner_team": "@googleapis/cloud-retail-team"
 }