Results from listing avatars should be paginated

[jwir3]

We need to return a set of pages of data from GET /avatars, rather than all of the data. #7 helps with this, since the data uris are no longer being returned, BUT we should limit the number of results that are returned from this endpoint.

[jwir3]

See also how a pagination system could be designed here: https://stackoverflow.com/questions/70409364/is-it-possible-to-get-pagination-info-from-rust-pagination-query-result