[ECS] [request]: add ECS Service event related to ELB target groups

### Community Note

* Please vote on this issue by adding a 👍 [reaction](https://blog.github.com/2016-03-10-add-reactions-to-pull-requests-issues-and-comments/) to the original issue to help the community and maintainers prioritize this request
* Please do not leave "+1" or "me too" comments, they generate extra noise for issue followers and do not help prioritize the request
* If you are interested in working on this issue or have submitted a pull request, please leave a comment

**Tell us about your request**
The console of a ECS service have events related to the ELB target groups, but I do not get them through the event bridge.

For instance:
* `service XX deregistered 1 targets in target-group YYYYY`
* `service XX has begun draining connections on 1 tasks.`

**Which service(s) is this request for?**
ECS / AWS event bridge

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
I'm using event bridge to centralize logging of all our services.

**Are you currently working around this issue?**
I can try to get it through cloudtrail events.