Add deployment status events on deployment edit and creation

First check

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[X] I used the GitHub search to find a similar request and didn't find it.
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Prefect Version

2.x

Describe the current behavior

If I update a deployment (e.g. to change the related work pool) its status may change from ready to unready (and vice versa) but no deployment status event is created.

Describe the proposed behavior

Any time a deployment goes from ready to unready (and vice versa) we emit a deployment status event.

Example Use

I want to be sure my deployment is healthy so create an automation that notifies when it's unhealthy. I edit my deployment to a work pool that has a problem and do not notice it. I would expect a notification but would not get one.

Additional context

This affects proactive automations too. If I create a deployment and it stays in unready, it would not trigger an automation that was looking for a deployment in an unready state.

PrefectHQ / prefect