Non-HTTP/S "url" entries cause entire post to be rejected (blocks FEP-fffd)

The current draft of FEP-fffd proposes adding additional url entries to signal that a post is bridged from another protocol, like Nostr or AT. This requires using non-HTTP/S URIs, such as nostr: or at:, to identify objects on these alternate protocols.

There's no need for Pleroma to actually support this FEP, but currently Pleroma will reject any posts with a non-HTTP/S URI in url. This makes implementing FEP-fffd in other applications impractical because it will cause posts to be ignored by Pleroma.

Ideally, Pleroma would simply ignore url entries it does not understand, without rejecting a post entirely.