chore: add library type to .repo-metadata.json (googleapis#336)

Author: parthea

.repo-metadata.json

@@ -6,6 +6,7 @@
  "issue_tracker": "https://issuetracker.google.com/issues?q=componentid:190851%2B%20status:open",
  "release_level": "ga",
  "language": "python",
+ "library_type": "GAPIC_COMBO",
  "repo": "googleapis/python-spanner",
  "distribution_name": "google-cloud-spanner",
  "api_id": "spanner.googleapis.com",