This is a followup to running tests in serial in CI.
Since the API package cannot import anything outside of api/,
copy the ci.Parallel function into api/internal/testutil, and
have api tests use that.
- tg.Count defaults to tg.Scaling.Min if present (falls back on previous default of 1 if Scaling is absent)
- Validate() enforces tg.Scaling.Min <= tg.Count <= tg.Scaling.Max
modification in ApiScalingPolicyToStructs, api.TaskGroup.Validate so that defaults are handled for TaskGroup.Count and