[ECS] [request]: Add option to forward headers via ECS Service connect

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**Tell us about your request**
We are actively using ECS Service connect for our production workloads and came across a use case where we need some of headers from our previous proxies. By seeing the tightly coupled architecture of service connect, we can't find how to do that either in documentation or anywhere.
> Provide an option in ECS Service connect configuration to do so.

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

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
We need an option to forward certain headers which are useful for our other micro services. Currently only ECS Service connect specific headers are passed via proxy. Some of the real world examples include `X-Forwarded-IP` or `X-Real-IP` or `X-Amz-Trace-id`. These are some of the headers which are beneficial for analyzing.
We are getting `x-request-id` but it's of no use as this is not relevant to any other proxy information.
We tested it from our end and received these headers only
```
headers=[
{
x-request-id=some_id,
content-length=0,
host=host:port,
x-envoy-expected-rq-timeout-ms=15000,
accept-encoding=gzip,
user-agent=agent
}
]
```

**Are you currently working around this issue?**
None

**Additional context**
Adding to that, some of the things that might be highlighted here is.
- I think you should provide an option same as AWS ELB Attributes are there. Whether to Preserve some headers or append to them.
- Ask Users what headers are needed to appended.
- Redated headers
- Forward headers or not

**Attachments**
None