Skia autoroll PRs are allowed to auto-merge provided presubmits all pass. This should be enabled for pub autoroll PRs as well.

• created new GitHub account: https://github.com/flutter-pub-roller-bot
• updated cloudKMS key to a new PAT for the new account
• update recipe to stop passing deprecated CLI argument https://flutter-review.googlesource.com/c/recipes/+/46722
• Change pub roller bot to push to flutter-pub-roller-bot/flutter.git #129844
• public documentation https://github.com/flutter/flutter
• Add flutter-pub-roller-bot to list of auto_approval_accounts .github#25
• registor bot with go/github-robot-accounts
• get CLAbot approval b/290661269
• mark .ci.yaml target as non-bring-up re-enable "Linux packages_autoroller" #130088
• internal setup documentation cl/547246229