Add PubkyApp schemas

[SHAcollision]

Pre-submission Checklist

For tests to work you need a working neo4j instance with the example dataset in docker/db-migration

• Testing: Implement and pass new tests for all new code, while maintaining existing test suite, cargo test.
• Performance: Ensure new code has relevant performance benchmarks, cargo bench

[Nuhvi]

I think calling these "homeserver" schemas is confusing

[SHAcollision]

I think calling these "homeserver" schemas is confusing

What do you propose? From the point of view of Nexus this is how we deserialize the data we get from homeservers.

[Nuhvi]

@SHAcollision I suggest calling it PubkyDotApp or PubkyApp schemas... since that is what they are and where they are defined.

[SHAcollision]

PubkyApp

Makes sense, I renamed them all as PubkyApp models.