[lib] improve reaction message notification text

Summary:
Now that we only notify the author of the target message of a reaction message, we can update the notification text from "USER reacted to a message" to be "USER reacted to your message"

Linear Task: ENG-2616

Depends on D6186

Test Plan:
Please review the screenshots to see what my changes look like

Before:

After:

Reviewers: atul, tomek, ashraful, ashoat

Reviewed By: tomek, ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D6208