Addons: activating a version doesn't purge the cache

[humitos]

When the use activates a new version, the addons API response doesn't immediately reflect this change. This is because the API response is cached. However, triggering a purge on that project won't immediately work since the version won't be built=True at that point yet.

So, we need to figure it out how to purge the cache on "new active versions, but only once they have finished successfully". How we can detect this?