[ECS] [request]: Update (add/remove) ALB TargetGroups on a ECS Service that has been already created

### 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**
After an ECS Service is created there is no option to update/modify the ALB TargetGroups that are integrated with the service. In case there is a need to change the alb, running ECS Services need also to be replaced.

**Which service(s) is this request for?**
ECS (Both over ASG or Fargate)

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
We would like to have the ability to change the ALB and the TargetGroups that are integrated with an ECS Service that is already created previously.

**Are you currently working around this issue?**
Currently, when we introduce a new ALB (and new TargetGroups for that ALB) we provision new ECS Services from scratch.

**Additional context**
Anything else we should know? - No, nothing else.

**Attachments**
-NONE-