AutoJoinCommunityHandler handles the logic for getting the user to automatically join communites that are tagged to farcaster channels that the user follows.
In a subsequent diff we will update this logic so we background these communites/threads by default
Linear task: https://linear.app/comm/issue/ENG-7959/query-the-users-channels-that-they-follow-on-app-start + https://linear.app/comm/issue/ENG-7960/download-all-the-relevant-blobs-based-on-the-viewers-farcaster
Depends on D12064