Created an Emby Connect API with the required methods to orchestrate a set of calls towards
EmbyConnect to build a JellyseerrLoginResponse object. Added an EmbyConnect authentication call to
the Jellyfin login() method as the last authentication attempt, but only if the username is an email
address. Updated the post() method on the ExternalApi class to handle request bodies that need to be
x-www-form-urlencoded.

Fallenbagel#749

This refactor includes a change that adds a conditional arg to the ExternalApi get() method to
override the base url. This method was pre-existing and already used in the calls and method.

Fallenbagel#943

Reverting get() baseUrl overwrite in favour of a vanilla fetch() call

Fallenbagel#943