[lib] Include [creator/target]FID in messageContentForServerDB when update relationship op is farcaster_mutual

Summary:
Pretty self explanatory, we want to include these in content column so we can reconstruct rawMessageInfo from both client and serverDB.

Depends on D11650

Test Plan: Will create UPDATE_RELATIONSHIP message with operation = 'farcaster_mutual' and observe that row in messages table is correctly constructed before landing.

Reviewers: ginsu, tomek, varun, will

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11651