add script to populate with backfill

[alrocar]

@jlmadurga pinging you for awareness

• I'm adding jobs for the release lifecycle, so they can be run manually from GH - GL
• There's a new script to do a simple populate with backfill so it can be reused when it makes sense: For now the script needs to exist in the target repository so we need to think on a strategy to maybe create them on tb init or use them remotely.