RHDH Backstage Upgrade

Own version numbers. Which @backstage/* release a checkout sits on, which release it should move to, and everything that breaks in between.

Start here

1. Read package.json and backstage.json before changing any dependency.
2. Establish the target RHDH version. Prefer an explicit user or repository value; otherwise invoke /rhdh-context for the checked-in compatibility matrix. If it is unavailable, ask the user for the target RHDH and Backstage versions rather than guessing.
3. Report current versions and the proposed target before running a bump.

Route by outcome