simple json API endpoint to get a mapping of pkgbase to maintainers

[anthraxx]

User story:
I'd like to get a simple mapping from all pkgbase to their corresponding maintainers. With such a mapping I could wire up the bug-bot poc test application that is then able to assign maintainers to issues in all packaging repositories.
The bot would go through all package repositories and check if there are issues. For all issues, it would look up the maintainers that were returned for that pkgbase from Archweb and assigns the missing maintainers.

Example response:
keys as pkgbase with values as lists of maintainers:

{
  "linux": ["jelle", "anthraxx"],
  "fortune-mod": ["fourtrelis"]
....
}

[alerque]

Such an endpoint might be what @repology needs to display maintainer data too. Arch packages have been missing it since it wasn't easy to derive from the package database or any other endpoints with bulk access.