[experiments] Friend nicknames

When I was going through the hidden experiments menu, I've saw 'Friend Nicknames'. I enabled them. Now you can add nicknames to friends via a right-click.

API-wise, its simple.

PATCH https://discord.com/api/v9/users/@me/relationships/USER_ID
JSON Data:
If changing/adding a nickname: A JSON object with the property nickname set to the nickname (e.g. {"nickname":"nick"})
If removing a nickname: A JSON object with the property nickname set to null (e.g. {"nickname":null})