[lib] Added method to call edit_message endpoint

Summary: Added a new method to call edit_message endpoint to send edited messages to the keyserver.

Test Plan: Checked if the app still works. Other tests are in later diffs.

Reviewers: michal, inka, ginsu, ashoat

Reviewed By: ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7139