Option to make Webhook User names configurable

[theCapypara]

Is your feature request related to a problem? Please describe. Kinda. This is related to #334. At the moment it is really simple for a matrix user to pretend to be somebody else just by changing the profile picture and nickname on matrix, since on Discord only these two things are shown.

Describe the solution you'd like Currently the nicks and usernames of ghosts on Matrix can be configured with a pattern. Add the same options for the Discord webhook.