Flask-digestauth

* Removed the test client. You should use httpx instead of Flask-Testing when writing automatic tests. Flask-Testing is not maintained for more than 3 years, and is not compatible with Flask 3 now.
* Revised to skip the tests when Flask-Login is not compatible with Werkzeug.

* Changed logging from STDERR to the Flask logger.
* Test case updates:
* Added missing documentation.
* Changed properties from public to private.
* Disabled logging.

* Revised the code for the upcoming Werkzeug 2.4.

* Updated the minimal Python version to 3.8.
* Switched from setup.cfg to pyproject.toml.
* Added the change log.
* Simplified README.rst.

* Added the DIGEST_AUTH_REALM configuration variable as the recommended way to set the authentication realm.
* Changed the default realm from an empty string to "Login Required".

* Changed the package name from flask-digest-auth to Flask-DigestAuth, according to the Flask recommended extension guidelines https://flask.palletsprojects.com/en/latest/extensiondev/ .
* Replaced app.digest_auth with app.extensions["digest-auth"] to store the DigestAuth instance.
* Replaced auth.app with current_app, to prevent circular imports.