chore(java-pubsub): add library to generation_config.yaml

Author: chingor13

generation_config.yaml

@@ -2019,6 +2019,27 @@ libraries:
   GAPICs:
   - proto_path: google/cloud/security/publicca/v1beta1
   - proto_path: google/cloud/security/publicca/v1
+- api_shortname: pubsub
+  name_pretty: Cloud Pub/Sub
+  api_reference: https://cloud.google.com/pubsub/
+  product_documentation: https://cloud.google.com/pubsub/docs/
+  client_documentation: https://cloud.google.com/java/docs/reference/google-cloud-pubsub/latest/history
+  api_description: is designed to provide reliable, many-to-many, asynchronous messaging
+    between applications. Publisher applications can send messages to a topic and
+    other applications can subscribe to that topic to receive the messages. By decoupling
+    senders and receivers, Google Cloud Pub/Sub allows developers to communicate between
+    independently written applications.
+  issue_tracker: https://issuetracker.google.com/savedsearches/559741
+  release_level: stable
+  language: java
+  distribution_name: com.google.cloud:google-cloud-pubsub
+  codeowner_team: '@googleapis/pubsub-team'
+  api_id: pubsub.googleapis.com
+  library_type: GAPIC_COMBO
+  requires_billing: true
+  recommended_package: com.google.cloud.pubsub.v1
+  GAPICs:
+  - proto_path: google/pubsub/v1
 - api_shortname: rapidmigrationassessment
   name_pretty: Rapid Migration Assessment API
   product_documentation: https://cloud.google.com/migration-center/docs