Implement petnames

[GBKS]

People can add "petnames" in contact lists (specs). Those should be used if available, which might mean that sometimes it's not necessary to load the whole profile.

Need to figure out how to balance using the logged-in users petnames vs. petnames the profile owner has assigned.

One of the issues is that most follow lists out there don't implement relays and petnames at all. They are just lists of npubs. This begs the question where it might not be helpful to add this to the profile health check (#35). It could also review your follow list and ensure it's complete.