[lib] process Inbound P2P messages on app start

Summary:
ENG-8902.

Depends on D13047

Test Plan:

1. Kill app after decrypting but before processing (adding sleep)
2. Open and make sure message is processed

Reviewers: tomek, bartek

Reviewed By: tomek, bartek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D13049