[ECS Service Connect] [Load Balancer Algorithm]: Allow customization for the load balancing algorithm

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**Tell us about your request**
Currently the load balancing algorithm is hard-coded to `round_robin` whenever ECS Service Connect is used. It would help to expand this to allow `least_outstanding_requests` similarly to what the ALB can currently offer.

**Which service(s) is this request for?**
ECS Service Connect

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
The end goal would be to distribute load more efficiently given that ECS Service Connect behaves as a service mesh for ECS.

**Are you currently working around this issue?**
By over allocating resources to account for any containers close to 100% even if the load in the cluster is in average under the desired auto scaling limit.

**Additional context**
N/A

**Attachments**
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