Subscriptions: remove old code

[stsewd]

We are now fully using dj-stripe for subscriptions, so we can our code for that. I'm not fully removing the app yet, so we can do a remove the old tables with zero downtime.

• Currently, we can "lock" subscriptions, this is we never disable the organization, even if the subscription ended.
  Went ahead and moved this to be an attribute of the organization instead.
• All querysets now use the dj-stripe models.
• All subscriptions are canceled now when the organization is deleted, previously this happened when the subscription model was deleted, but now we aren't using those anymore.
• A new handler for when a subscription is created was added, so in case we manually create a subscription for the user, this is reflected in the organization.
• Other handlers were updated to take into consideration a change in subscriptions, and re-enable organizations is case the subscription is changed to active. I think we should be covered now for all cases when managing the subcriptions from stripe, no need to touch the django admin (hopefully).
• test_daily_email was renamed to test_tasks, since we were testing that.
• There was a problem with the CI using an old cache, our pre-commit setup depends on the testing requirements, so I added that file to the cache key.

After this is deployed, we can zeroed the migrations and remove the app.

How to deploy this change

• Deploy web-extra
• Run the migrations in web-extra
• Run the following code

Organization.objects.filter(subscription__locked=True).update(never_disable=True)

• Continue as usual

Closes #10624

[humitos]

This looks pretty good! I wasn't able to review everything yet, tests are missing still, but the core logic is 👍🏼 . I left some feedback as well.

I'll come back with fresh eyes for the tests in the following days.

[humitos]

Why do we need both here, disable_soon and subscription_trial_plan_ended?

[stsewd]

We are automatically disabling expired trial subscriptions only, we don't do that automatically for normal subscriptions (I think we should start doing it automatically as well)

[humitos]

Thanks for considering all my suggestions 👍🏼