FEP-1d80: Feed Actor - a way to federate a collection of Group actors

[jollyroberts@socialhub.activitypub.rocks]

Over at PieFed we, like Lemmy and Mbin have gotten requests for a way to have a grouping of communities type feature.

We experimented with trying to use the existing Group actor, but found that it was not a perfect fit. So we decided that a new AP Actor was the way to go.

The linked Fep PR defines the Feed actor, based on how its working in production on Piefed instances.

WIP FEP PR