Flexible Search

[ShadowJonathan]

This is an addon to https://github.com/buresdv/Mlem/issues/83.

Since the API is able to have powerful search, I think it'll be interesting to allow search UX such as (but not limited to);

• Searching posts across communities (by title, description, user, etc.)
• Searching comments across communities (by content, user, etc.)
• Searching users
• Searching communities (this is probably https://github.com/buresdv/Mlem/issues/92)