XRayConfig_SegmentFields can't be configured correctly from an xDS control plane

Title: XRayConfig_SegmentFields can't be configured correctly from an xDS control plane

Description:

Currently the XRayConfig_SegmentFields.Origin and XRayConfig_SegmentFields.Aws fields will allow configuring that the trace segment comes from the correct origin as per the Optional Segment Fields in the AWS Segment fields documentation.

The aws object that needs to be sent to make this origin be considered valid requires the following data:

ecs – Information about an Amazon ECS container.
- container – The hostname of your container.
- container_id – The full container ID of your container.
- container_arn – The ARN of your container instance.

This is possible to do using sed and yaml on statically configured envoy hosts.

However, an xDS server cannot populate this with meaningful data and it should be handled internally by envoy's XRay tracing features. I believe that detecting the correct data should be up to each individual envoy proxy at runtime, and should not be configurable here either in the yaml or in the xDS gRPC structs.

Relevant Links:

• https://github.com/envoyproxy/go-control-plane/blob/main/envoy/config/trace/v3/xray.pb.go#L109
• https://docs.aws.amazon.com/xray/latest/devguide/xray-api-segmentdocuments.html#api-segmentdocuments-fields