[sqlite] Rename getAllOutboundP2PMessages() to getUnsentOutboundP2PMessages()

Summary:
https://linear.app/comm/issue/ENG-9291/read-outbound-messages-with-status-different-that-sent

getAllOutboundP2PMessages() no longer returns all messages, but only unsent messages. As this name
may be misleading, maybe it'd be nice to rename it.

Depends on D13908

Test Plan: Run the app and send some messages on web and native.

Reviewers: tomek, kamil

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D13909