feat(auth): refactor auth, add oidc

Thanks to all HedgeDoc team members for the time discussing,
helping with weird Nest issues, providing feedback
and suggestions!

Co-authored-by: Philip Molares <philip.molares@udo.edu>
Signed-off-by: Philip Molares <philip.molares@udo.edu>
Signed-off-by: Erik Michelson <github@erik.michelson.eu>

backend/test/private-api/auth.e2e-spec.ts

@@ -278,7 +278,7 @@ describe('Auth', () => {
         await request(testSetup.app.getHttpServer())
           .delete('/api/private/auth/logout')
           .set('Cookie', cookie)
-          .expect(204);
+          .expect(200);
       });
     });
   });