[lib] introduce DispatchMetadata for Inbound and Outbound actions

Summary:
ENG-8423.

This improves types and naming to reflect rest of the codebase.

SCHEDULE_P2P_MESSAGES is no longer needed, P2P messages are now part of PROCESS_DM_OPS.

Depends on D13151

Test Plan:
Flow

Note: This stack is tested end-to-end according to the process described here.

Reviewers: tomek, inka

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D13152