To validate the username when creating services

[viggy28]

Recently I encountered a situation where the username is empty and currently backend only does whether the username matches the JWT or not but it doesn't validate the username itself (like its empty or special characters) etc.

cc @rajatmaheshwari2512 on the side note, it also seems like a bug in the frontend (because in the first place we shouldn't let create service from not actively signed-in user. It's gonna be a little hard to reproduce the situation)