feat: STACKIT Workflows Integration

[c-thiel]

Description

Adds the STACKIT Workflows SDK at v0.1.0. Backend for upcoming workflows resources in terraform-provider-stackit (managed Airflow orchestration).

Generated code in services/workflows/v1alphaapi/ produced by the OAS bot from stackitcloud/stackit-api-specifications (commit d2755fb2bda0e2105f920af64d7176d184b2bcb7). On top of that:

• v0.1.0 release artifacts (CHANGELOG.md, VERSION, NOTICE.txt)
• LICENSE.md copyright fill (generator shipped Apache placeholder Copyright [yyyy] [name of copyright owner])
• wait/ subpackage — CreateInstanceWaitHandler (20m), UpdateInstanceWaitHandler (15m), DeleteInstanceWaitHandler (15m), following the modern WaiterHelper pattern used by dremio and
  telemetrylink - Usage example at examples/workflows/
• Root + per-service CHANGELOG entries

DAG bundle CRUD is synchronous per the OAS contract (201/200/204, no Operation handle, no status field on DagBundleResponse), so no bundle waiters ship in v0.1.0. If async semantics are introduced, the OAS should be updated first and bundle waiters added then.

Supersedes the auto-generated PR #7723 (and the older #7695, #7709) — those should be closed in favor of this one, matching the dremio v0.1.0 pattern in #7166.

Verified end-to-end against eu01

Both the wait helpers and the canonical example file were exercised against
the live API:

[+28s] Create accepted id=6a634d9f-... status=creating
[+3m8s] Create active endpoint=https://...workflows.eu01.stackit.cloud/
[+3m11s] Update done
[+4m42s] Delete done

Wait timeouts have 7–10× headroom over observed times.

Known caveats for v0.1.0 consumers

STACKIT IdP variant (StackITIdentityProvider) is not yet supported by the deployed backend; instances need an OAuth2IdentityProvider block. The Workflows team is actively working on STACKIT IdP support.

Checklist

• Issue was linked above (supersedes Generator: Update SDK /services/workflows #7723)
• No generated code was adjusted manually (check comments in file header)
• Changelogs
  • Changelog in the root directory was adjusted (see here)
  • Changelog(s) of the service(s) were adjusted (see e.g. here)
• VERSION file(s) of the service(s) were adjusted
• Code format was applied: make fmt
• Examples were added / adjusted (see examples/ directory)
• Unit tests got implemented or updated
• Unit tests are passing: make test (will be checked by CI)
• No linter issues: make lint (will be checked by CI)