Write additional hand crafted samples for Pub/Sub

The critical samples are complete (#3017).

The remaining samples are listed here. If you are choosing to add one, please create a sub-issue from the task item and assign yourself.

### Publish

- [ ] `pubsub_publish`
- [ ] `pubsub_publish_avro_records`
- [ ] `pubsub_publish_proto_messages`
- [ ] `pubsub_publish_custom_attributes`
- [ ] `pubsub_publish_with_error_handler`
- [ ] `pubsub_publish_messages_error_handler`
- [ ] `pubsub_publish_otel_tracing`
- [ ] `pubsub_publisher_with_compression`
- [ ] `pubsub_publisher_flow_control`
- [ ] `pubsub_publisher_concurrency_control`

### Subscribe

- [ ] `pubsub_subscriber_async_pull`
- [ ] `pubsub_subscriber_sync_pull`
- [ ] `pubsub_subscriber_async_pull_custom_attributes`
- [ ] `pubsub_subscribe_avro_records`
- [ ] `pubsub_subscribe_avro_records_with_revisions`
- [ ] `pubsub_subscribe_proto_messages`
- [ ] `pubsub_subscribe_otel_tracing`
- [ ] `pubsub_optimistic_subscribe`

### Admin (Topics, Subscriptions, & Schemas)

- [ ] `pubsub_update_topic_type`
- [ ] `pubsub_update_topic_schema`
- [ ] `pubsub_get_topic_policy`
- [ ] `pubsub_set_topic_policy`
- [ ] `pubsub_test_topic_permissions`
- [ ] `pubsub_detach_subscription`
- [ ] `pubsub_get_subscription_policy`
- [ ] `pubsub_set_subscription_policy`
- [ ] `pubsub_test_subscription_permissions`
- [ ] `pubsub_create_push_subscription`
- [ ] `pubsub_create_unwrapped_push_subscription`
- [ ] `pubsub_update_push_configuration`
- [ ] `pubsub_create_bigquery_subscription`
- [ ] `pubsub_create_cloud_storage_subscription`
- [ ] `pubsub_create_subscription_with_filter`
- [ ] `pubsub_dead_letter_create_subscription`
- [ ] `pubsub_dead_letter_update_subscription`
- [ ] `pubsub_dead_letter_remove`
- [ ] `pubsub_create_topic_with_schema`
- [ ] `pubsub_create_topic_with_schema_revisions`
- [ ] `pubsub_create_topic_with_cloud_storage_ingestion`
- [ ] `pubsub_create_topic_with_kinesis_ingestion`
- [ ] `pubsub_create_topic_with_aws_msk_ingestion`
- [ ] `pubsub_create_topic_with_azure_event_hubs_ingestion`
- [ ] `pubsub_create_topic_with_confluent_cloud_ingestion`
- [ ] `pubsub_create_proto_schema`
- [ ] `pubsub_commit_avro_schema`
- [ ] `pubsub_commit_proto_schema`
- [ ] `pubsub_get_schema_revision`
- [ ] `pubsub_rollback_schema`

These samples were identified in: https://github.com/googleapis/google-cloud-rust/issues/3017#issuecomment-3293254090