feat: allow disabling user tours

[Agrendalath]

Description

Currently, there is no way to disable user tours. There used to be a similar waffle flag, but it was dropped in 2038633.

Supporting information

Link to other information about the change, such as Jira issues, GitHub issues, or Discourse discussions.
Be sure to check they are publicly readable, or if not, repeat the information here.

Testing instructions

1. Run the following snippet in the Django shell:

    from django.contrib.auth.models import User
    from lms.djangoapps.user_tours.models import UserTour
   
    UserTour.objects.update_or_create(user=User.objects.get(username='edx'), defaults=dict(course_home_tour_status='show-new-user-tour', show_courseware_tour=True))

2. Log in as an edx user.
3. In LMS, visit the Course Outline page of the Demo course and see that the user tour is displayed.
4. Create a Waffle flag (/admin/waffle/flag/) called user_tours.tours_disabled and set it to Yes.
5. Load the Course Outline page again and see that the tours are no longer displayed.

Deadline

"None"

Other information

Private-ref: BB-8396

[openedx-webhooks]

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[navinkarkera]

@Agrendalath Looks good.:+1:

• I tested this: (Disabled tours in my local setup using the flag)
• I read through the code

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[edx-pipeline-bot]

2U Release Notice: This PR has been deployed to the edX staging environment in preparation for a release to production.

[edx-pipeline-bot]

2U Release Notice: This PR has been deployed to the edX production environment.

[edx-pipeline-bot]

2U Release Notice: This PR has been deployed to the edX production environment.