Display federation restrictions

Similar to how pleroma-fe displays federation restrictions on /about, I think we should do the same.

Might need to pull instance data from /nodeinfo/2.0.json instead of /api/v1/instance in order to get the federation restrictions.

Also need to consider how to incorporate it with the idea of having custom configurable pages. If About is a configurable page, how can we (or should we?) inject something like federation restrictions into it?