[FastAPI] Rename the `credentials` methods
Currently, within aurweb, we use a number of "credentials" to perform permission checks for different parts of the website. As @jelle has pointed out, this is a bit confusing, because in most web applications, credentials is used as a term for things provided to login or gain authentication in some way.
We'd like to change the way we call these credentials to make a bit more sense.
One suggestion that sounds quite good is permissions
.