Replace QTWebEngine-based login flow with Globus native login.

[mikedarcy]

The use of the embedded Chromium browser in QT5 (QtWebEngine) by deriva-auth is and has been problematic for a few reasons.

First, the bundling environment (cx_freeze) has had trouble with it in the past and may again in the future. Second, the whole idea of embedding a web browser into a frozen bundled environment is dangerous due to the relative lag in being able to apply browser vulnerability patches, since we have to wait for Qt and PyQt releases. Granted, our use of the browser is very limited (i.e., we just use it for login flows), but still, it would be better to not have a dependency on this component, if there are alternatives.

If we change the login flow to use the Globus native-app login via our globus_auth_utils library, the UX would likely be very similar and we would just leverage whatever the default browser on the system is. This needs more investigation and some prototyping, but there is a potential way forward here.