Add datumctl iam service-accounts command family

[ecv]

Summary

datumctl has no iam service-accounts command family. Add commands to manage IAM service accounts (create / list / get / delete, and key/token management as applicable) on Datum control planes.

Motivation

The infra Chainsaw e2e suite has a service-account-lifecycle unit test that is currently skip: true because it depends on datumctl iam service-accounts commands that do not exist:

• datum-cloud/infra tests/unit/iam/service-account-lifecycle/chainsaw-test.yaml
• Tracked in datum-cloud/infra#2806 and datum-cloud/infra#2733

The test stays skipped until this command family ships.

Notes

• Not slated for the near term — this issue exists to track the dependency, not to schedule it.
• Un-skipping the infra test is the acceptance signal once commands land.

Refs

• datum-cloud/infra#2806
• datum-cloud/infra#2733