Added Friend Sound Plugin

[Martyrshot]

This plugin allows users to assign mp3s to play when a "username has logged in." message is displayed in game. It was designed to mimic a walk up song that a baseball player has when they go up to bat while playing at home.

[runelite-github-app[bot]]

New plugin marty-walkup: https://github.com/Martyrshot/runelite-marty-walkup/tree/e7b013b31d3181e4aa0d36d805db90818b6e1b3b