User rating

[Catrya]

After a successful trade Mostro send a nip59 event to both parties to let them know they can rate each other. The client must receive user's input (a number between 1 and 5) and create a new nip59 event to send to Mostro with the rate.
Mostro will send back a confirmation message to the user with the rate.

Reference: https://mostro.network/protocol/user_rating.html
Must adhere to this design.