Addressable interacted collection

[fauno]

Now that we have the interacted collection, it'd be great to be able to address it on audience/to/cc attributes. An use case that comes to mind is to send Actor Update's, so remote instances renew their caches, specially on keypair rotation.

[fauno]

Related to #32

[fauno]

@RangerMauve suggested today to make the magic Public URL addressable and internally map to the interacted collection. It makes sense to me because it's the public we know of.

When the Public/interacted collection becomes addressable, we can send out Delete(Actor) when an account is blocked.