chore(.github): update CODEOWNER for Data Analytics clients
* @codyoss @tbpg
/bigtable/ @tritone
-/bigquery/ @shollyman
+/bigquery/ @googleapis/api-bigquery
/datastore/ @tritone
/firestore/ @tritone
-/pubsub/ @hongalex
+/pubsub/ @googleapis/api-pubsub
/spanner/ @skuruppu
/storage/ @tritone
