Clean-up development (branch) packages in phoenix-dev channel

The workflow that creates packages for each branch of each phoenix repository will quickly create a ton of packages that we don't want to keep. It is required to implement a clean-up bot to remove them before the channels gets too large.

We should do something similar to the gitlab clean-up rules for the container registry:

• keep at least N dev packages per repository (N=5?)
• keep the release packages (nothing to do, they are in a different channel)
• keep at least M most recent packages
• remove the rest

Note: the clean-up bot will operate on a channel containing all the phoenix packages (unlike the container registries examples that we have now that operate at project level), so it may require a list of projects (projects name?) to not mess-up packages names and branch names.