Support awsxray trace propagation format

[jholm117]

What problem are you trying to solve?

Currently, Linkerd only supports B3 and w3c for trace propagation headers.
My applications use aws xray, conversely.

How should the problem be solved?

Linkerd supports aws xray

Any alternatives you've considered?

I could add a service to translate my trace headers to xray before they hit linkerd but I'd rather not if possible.

How would users interact with this feature?

linkerd would automatically detect which format is being used. The user doesn't need to do anything.

Would you like to work on this feature?

yes