Hastexo-xblock

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* [Bug fix] Retry `read_from_contentstore()`. Use `tenacity`'s
retry functionality for getting course information from contentstore.

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* [Bug fix] From Celery 5.0.0 the legacy task API was discontinued.
This meant that the Task base class no longer automatically registered
child tasks in Open edX Nutmeg (which uses Celery 5.2.6).
Manually register the class-based tasks on the Celery app instance.
* [BREAKING CHANGE] Update the `hastexo_guacamole_client` to
Channels 3. The asgi root application (`ASGI_APPLICATION`)
is now defined in the `asgi.py` file instead of `routing.py` file.
The asgi application now also checks for allowed hosts,
meaning if you want to allow the LMS to connect to labs via the `hastexo_guacamole_client`, the LMS host has to be listed in
`ALLOWED_HOSTS` at `hastexo_guacamole_client.settings.py`.
* [Documentation] Remove obsolete deployment instructions for the
old “native” (Ansible-based) installation, and the old Devstack.

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* [Enhancement] Add an option to override the `suspend_timeout`
global setting via an XBlock attribute, in seconds.

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* [Bug fix] Fix migrations around the `lab_usage_limit` feature
introduced in 6.1.0. This unbreaks migrations in the event that some
stacks cannot be linked to an existing user account.

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* [Bug fix] Bring back `asgiref` constraint and lower
`Django` constraint. These need to be
in sync with the `channels` version requirements.

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* [Bug fix] Add a check to the `add_user_foreign_key` migration
file to find stacks that are missing a link to a real user account.
If such stack(s) exist, do not attempt to apply the migration,
instead raise an exception and provide an error message with
guidance on how to proceed.