Add farcaster contest bot

[rbennettcw]

Link to Issue

Closes: #10302

Description of Changes

• Adds FC contest bot that posts a confirmation message when the user has added content to a contest
  • Also posts message if user isn't eligible to add content (no verified address)

Test Plan

• Set NEYNAR_API_KEY and NEYNAR_BOT_UUID envs (ping me if needed)
• Make FC contest, post contest, post reply, wait a few seconds until content projection is saved, confirm that bot sends reply message to content cast

Deployment Plan

• In Neynar dashboard, ensure that the QA/Production apps have a generated bot (requires signing wallet), get the bot UUID
• Set env NEYNAR_BOT_UUID to bot UUID

Other Considerations

• The issue with having the bot send error messages is that we often retry failed policies, so if the bot responds naively to failure, it'll repeat the same message 3 times. We could either prevent the failures from retrying (via ack), or track failure count in the DB. Neither solution is ideal.

[timolegros]

2 nits - haven't tested