Add example for `config set --auth.method=hook` in docs

[SuitDeer]

Hi I had trouble to find information about the hook authentication method. It would be cool if it would be explained in the following document:
configuration/authentication-method.md

I have found some information in the following merge request:
filebrowser/filebrowser#1554

And I have written a example of a LDAP authentication method via the hook authentication method. (That could be added as a hook authentication method into the docs):

filebrowser/filebrowser#3702