tracking issue to successfully generate several API clients

This is a tracking issue for API clients for the Dart backend to generate; these clients may excercise various generation features we haven't seen before:

- [x] `google.cloud.aiplatform.v1`
- [x] `google.cloud.redis.cluster.v1` googleapis/google-cloud-rust#1088
- [x] `google.monitoring.v3` googleapis/google-cloud-rust#827
- [x] `google.monitoring.metricsscope.v1` googleapis/google-cloud-rust#832
- [ ] `google.cloud.sql.v1` googleapis/google-cloud-rust#769
- [ ] `google.cloud.bigquery.v2` googleapis/google-cloud-rust#829
- [ ] `google.cloud.gsuiteaddons.v1` googleapis/google-cloud-rust#1278
- [ ] `google.cloud.gkehub.v1` googleapis/google-cloud-rust#1249
- [ ] gapic showcase; https://github.com/googleapis/google-cloud-rust/blob/main/src/generated/showcase/.sidekick.toml