Removed unused imports from lms/envs

Close https://github.com/openedx/build-test-release-wg/issues/10

Currently the registration endpoint has no rate limit. Added a new ratelimit
variable to support the change, it's value is set to 60/7d.

VAN-302

Fixes an issue where the button that linked to edX documentation for
course teams in Studio that displayed beside the logged-in user's username/
drop-down menu is gone. Regression from PR #26106

Ref: TNL-8138

#27097 reverted the pylint amnesty change. After reverting the ubuntu20 deployment, now this can be deployed again.

Updates the annotations for the block structure settings and toggles based on a [discussion] that was held on the pull request that annotated those same settings and toggles.

It also adds the DEPR tickets that were promised earlier in the annotations.
For future reference, there's also a [forum thread] to discuss the DEPR tickets titled.

[discussion]: https://github.com/edx/edx-platform/pull/26175#issuecomment-800632485

[forum thread]: https://discuss.openedx.org/t/deprecation-removal-several-block-structure-caching-settings-depr-143-depr-144-depr-145-depr-146/4288?u=nizar

Adds logging and monitoring capabilities for expected
errors. See the ADR and how-to  documentation for
details of how to configure and use the EXPECTED_ERRORS
setting and new monitoring and logging.

ARCHBOM-1708

Co-authored-by: Tim McCormack <tmccormack@edx.org>

* Add toggle and settings annotations for CCX

Co-authored-by: Robert Raposa <rraposa@edx.org>

The setting overrides should've been cleaned up in a previous
commit, but I missed them. This change is a no-op.

Previously, deprecated [lms|cms|common]/djangoapps
import paths would only raise errors if the
ERROR_ON_DEPRECATED_EDX_PLATFORM_IMPORTS
flag, which defaulted to False (but is overriden
to True for Devstack and *.edx.org), was enabled.

This change removes that setting and always raises
on use those deprecated import paths.

S3 URLs served by Blockstore have a max TTL of
1hr, since the temporary credentials the Blockstore
uses to sign the URLs themselves have a TTL of
1hr. Thus, we must cache Blockstore bundles for
less than 1hr.

TNL-7771

The Django setting
FEATURES['ENABLE_COURSEWARE_MICROFRONTEND']
has been an additional gate to activating
usage of the Learning MFE for an Open edX
instance.

The toggle is redundant with the
`courseware.courseware_mfe`
Waffle flag. By removing it, we simplify our config
and simplify our path towards making the Learning MFE
the default courseware experience.

TNL-7796

See DEPR-142

docs: added detailed description for the AUTOMATIC_AUTH_FOR_TESTING feature flag annotations

This minimizes our footprint outside of the djangoapp, now and moving
forward. Not only can we drop the `lms/envs/common.py` change, but we
can also avoid touching `lms/urls.py` when we add the API. Everything
can stay contained within `openedx/core/djangoapps/discussions`.

VAN-312

This reverts commit fc06846c.

* pyupgrade in lms dir

* replace wildcard

* pep8 fix

* fix quality

See DEPR-142

This reverts commit 0517603b.

This was masking a LabXchange error by blowing up with:
"Stack trace builtins:AttributeError: 'NoneType' object has no attribute 'status_code'"

The mobile app is getting unexpected 403s from
/oauth2/exchange_access_token/, but we have been unable
to pinpoint from where they are coming. This commit
introduces a temporary exception handler to provide stack info
for 403s on this endpoint to try to track down the source.

Requires the ENABLE_403_MONITORING setting to be set to
True to enable the logging.

ARCHBOM-1667

We use django-ratelimit to limit per IP login attempts, and then we use
django-ratelimit-backend to limit per username login attempts. This
change replaces the usage of django-ratelimit-backend with another
instance of django-ratelimit so that both limits can be managed by one
library.

This is the first step in being able to fully excise
django-ratelimit-backend from edx-platform. Note that we're still using
the `RateLimitMixin` in openedx/core/djangoapps/oauth_dispatch/dot_overrides/backends.py
because studio and the admin UI still relies on that for rate limiting.
Those login paths will have to be updated before we can remove the mixin
from our auth backend.

docs: added related settings description for login attempts