Adopt image.source in modules/bi/superset/module.yaml

[RonaldHensbergen]

Part of #407, depends on #532 (renderer mechanism/first adopter in Dagster must land first so the pattern is proven).

Scope

1. Add the same image.source (enum build/registry, default build) and image.tag config to modules/bi/superset/module.yaml's configSchema, reusing the mechanism built in image.source: build|registry — renderer mechanism to emit image: instead of build: #532 rather than duplicating logic.
2. Superset's image: naming/tag scheme differs slightly from Dagster's (see .github/workflows/publish-images.yml's per-image "Determine version" step, which derives Superset's base version from apache/superset:<version> rather than a pip package version) — confirm the registry image reference this module emits matches what publish-images.yml actually publishes for cds-superset.
3. Unit tests in tests/test_renderer.py/tests/test_planner.py mirroring image.source: build|registry — renderer mechanism to emit image: instead of build: #532's Dagster coverage, for Superset.
4. Consider (but don't require) whether the image.source/image.tag schema fragment should be factored into a shared JSON Schema definition reused by both modules, now that two modules use it — if straightforward, do it here; otherwise file a follow-up.

Relationship

Parent issue: #407. Depends on #532.