Create close/open events for Pull Requests and Issues

[uesteibar]

Expected Behavior

Pull Requests and Issues should be mapped to two events:

• Creation
• Closing/Merging (only if it already happened)

Current Behavior

Currently we only map the open event.

Possible Solution

The api provides a state field with which we can know if if was already closed or merged.
We also have closed_at and merged_at to add the timestamp.
In the case of a merge event, we also have a merged_by field with the user that did it.