[lib][keyserver] Add editing message type to messageTypes

Summary:
Registered new message type EDIT_MESSAGE to messageTypes. Added some lines to prevent flow-typing errors in different places of the app. For now, when we process the added
message type, we ignore it.

Test Plan: Tested if app compiles and checked if everything works correctly.

Reviewers: michal, inka, ginsu

Reviewed By: ginsu

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D6962