Fix logout

[ramortegui]

This PR fixes the logout functionality, related to: https://github.com/ueberauth/ueberauth_example/issues/49 https://github.com/ueberauth/ueberauth_example/issues/29

• Use a form to include all the required data and action to do a delete
• Update the delete function on the controller to use clear_session instead of configure_session [1]

Also, updates config/test adding username and password fields that needed to be passed to the GitHub Actions container for testing.

[1] https://stackoverflow.com/questions/42910224/put-flash-not-works-with-configure-sessiondrop-true

[doomspork]

Thank you thank you @ramortegui :pray: