feat: third party authentication automatic logout with a single redirect

[CefBoud]

Description

Current Third Party Authentication logout requires a redirect from the SSO IDP to the LMS to handle IDAs logout, i.e. we need to visit the <LMS>/logout twice. This PR attempts to handle the TPA logout with only one visit to <LMS>/logout.

Testing instructions

1. Add TPA_AUTOMATIC_LOGOUT_ENABLED = True to edx-platform/lms/envs/devstack.py
2. Replace self.tpa_logout_url = tpa_pipeline.get_idp_logout_url_from_running_pipeline(request) in edx-platform/openedx/core/djangoapps/user_authn/views/logout.py with self.tpa_logout_url = "https://example.com/logout" (to simplify testing)
3. Launch LMS and Studio e.g. make dev.up.lms+cms
4. Check the network tab and ensure that the user is logged out from both the LMS and Studio before being redirected to https://example.com/logout (fake IDP logout URL)

Supporting information

Private ref BB-8759

Deadline

"None" if there's no rush, or provide a specific date or event (and reason) if there is one.

[openedx-webhooks]

Thanks for the pull request, @CefBoud!

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[CefBoud]

This is ready for review.