Simplify -fasttrack vs -backports-staging criteria for bookworm

I was discussing the criteria for choosing -fasttrack vs -backports-staging with @rmb and I think for bookworm, we can simply it.

1. things official backports team don't want goes to -fasttrack
2. things we don't want to upload to official -backports for various reasons goes to -backports-staging

comments?

Currently ruby and any packages that needs a rebuild with new ruby (or packages that depend on packages that needs rebuild) also goes to -fasttrack