feat(github): allow users to uninstall github from Sentry

[scefali]

Historically, we have prevented users from uninstalling Github from Sentry because there is still an installation on the Github side. We forced users to uninstall from Github which triggers a webhook to disable the integration in Sentry. Only at that point could a user remove the integration. However, this is proving problematic because sometimes integrations get in a bad state and it would be better to just remove the installation (and sometimes reinstall).

In the new flow, users can always uninstall the Github integration from Sentry. When that happens, the app is still installed on Github's side but we remove the OrganizationIntegration row and remove the integration_id on the attached repos. If the user wants to reinstall then they would uninstall and reinstall in Github. Those repos which were unattached automatically get reattached to the new integration. So there isn't really a downside to letting the user uninstall in Sentry (things won't get into a bad state).

I've also fixed a KeyError in Sentry when the webhook tries to remove an integration that doesn't exist (SENTRY-CF1).

Fixes: #20599

[mgaeta]

I'd explicitly set can_disable to false and leave comment describing the user issue.
Also the comment above IntegrationProvider.can_disable doesn't really describe what disabling does.

[MeredithAnya]

I agree it's a little confusing because technically the integration can still be set to disabled if the user uninstalls from GH first. But we use this attribute for whether or not we show the disable dialog text.

I think we should really be documenting the install and uninstall flows for our integrations and related data (i.e. repos, commits, alert rules)

[scefali]

@MeredithAnya @mgaeta I added a new comment in the base class what can_disable actually does

[MeredithAnya]

For anyone who is curious, the organization_integration_details.py delete endpoint ends up calling a task that resets the integration_id to None:

sentry/src/sentry/tasks/deletion.py

Lines 379 to 381 in 3eeb60e

	Repository.objects.filter(
	organization_id=instance.organization_id, integration_id=instance.integration_id
	).update(integration_id=None)

The reason the repos get reattached is that we added the post_install method that does the work of finding the "orphaned" repos and giving them back their integration_id

sentry/src/sentry/integrations/github/integration.py

Line 167 in 3eeb60e

def post_install(self, integration, organization, extra=None):

[MeredithAnya]

I wish we could still link people to GH so that they uninstall over there. But not sure where that would go. And maybe we just see if that is even a problem

[scefali]

I wish we could still link people to GH so that they uninstall over there. But not sure where that would go. And maybe we just see if that is even a problem

Based on my testing, it's rather unnecessary IMO. Uninstalling from Github's side doesn't really provide any benefits.