Implement shared release workflow for solution-arsenal and artifact-conduit #42

solution-arsenal and artifact-conduit release in different ways:

• solution-arsenal: someone runs the Release workflow manually. It computes the version and notes with git-cliff, creates the tag and a draft release, and publishing the draft triggers Docker, Helm and docs.
• artifact-conduit: pushing a tag starts the release, and release-drafter writes the notes.

Move solution-arsenal's tooling into a reusable workflow in dev-kit and have both repos call it. Each repo keeps its own build jobs.

Acceptance criteria

• dev-kit has a reusable release workflow that does what solution-arsenal's Release workflow does today
• solution-arsenal uses the shared workflow, and its releases work the same as before
• artifact-conduit uses the shared workflow, release-drafter is removed, and its release builds run when a release is published instead of on tag push
• The release process is documented in dev-kit