AutoFlow: emit merge request related events

What does this MR do and why?

This change set introduces event dispatching of some merge request related events to AutoFlow. It's very similar to the merge request recently merged for issue-related events. See AutoFlow: emit issue-related events (!177277 - merged).

References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

• #508262 (closed)
• #443486

Testing

• You may setup AutoFlow in GDK as described in https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/autoflow.md or follow https://gitlab.com/-/snippets/4800564
• Enable feature flags (autoflow_enabled and autoflow_merge_request_events_enabled)
• Implement basic Flow script in some project in .gitlab/autoflow/main.star:

def output_event_data(w, ev):
    print("Handling test event: " + ev["type"] + " with data: " + str(ev["data"]))

on_event(
    type="com.gitlab.events.merge_request_created",
    handler=output_event_data,
)

on_event(
    type="com.gitlab.events.merge_request_updated",
    handler=output_event_data,
)

on_event(
    type="com.gitlab.events.merge_request_merged",
    handler=output_event_data,
)

on_event(
    type="com.gitlab.events.merge_request_closed",
    handler=output_event_data,
)

on_event(
    type="com.gitlab.events.merge_request_reopened",
    handler=output_event_data,
)

• Create, Update, Merge, Close and Reopen a merge request in that project
• Verify KAS output that you see the prints from the output_event_data handler of the Flow script.