Differentiate the expire from leave event

At the moment we cannot see whether a user left a project due to their membership expiring or if they themselves opted to leave the project. This adds a new event type that allows us to make this differentiation. Note that is not really feasible to go back and reliably fix up the previous events. As a result the events for previous expire removals will remain the same however events of this nature going forward will be correctly represented.

Closes #22611 (closed)

Restored source branch add_user_expire_leave_event

Added 1 commit:

• 346c9514 - Differentiate the expire from leave event

Added ~164274 label

@adamniedzielski as you added the expiration feature, would you like to take a look too?

It looks really good to me, thank you @callumdryden!

Added 255 commits:

• 346c9514...061d1e2d - 254 commits from branch gitlab-org:master
• 2f19cd88 - Differentiate the expire from leave event

Added ~480950 label

@callumdryden Awesome work, thanks!

Milestone changed to %8.13

Reassigned to @callumdryden

Added 1 commit:

• 25741ab7 - Differentiate the expire from leave event

Added 51 commits:

• 25741ab7...4e963fed - 50 commits from branch gitlab-org:master
• 8cfcba68 - Differentiate the expire from leave event

Thanks for the reviews guys @rymai I have tried to update the specs more in keeping with the style you suggested. Please let me know if you are happy with these changes.