fix(propagator-aws-xray): correctly propagate over grpc

[dweitzman-codaio]

Similar to open-telemetry/opentelemetry-js#2285 for the b3 propagator

Which problem is this PR solving?

Fixes open-telemetry/opentelemetry-js#4830

Short description of the changes

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: dweitzman-codaio / name: David Weitzman (35dbd46, ea0e07f)
• ✅ login: pichlermarc / name: Marc Pichler (24bd52f)

[dweitzman-codaio]

cc @dyladan since open-telemetry/opentelemetry-js#4830 is currently assigned to you

[pichlermarc]

Note: "unmaintained" label was applied incorrectly, @jj22ee is the owner.
I opened #2606 to address this.

[jj22ee]

LGTM. Can you add a test case for this fix, similar to the B3 one?

[dweitzman-codaio]

LGTM. Can you add a test case for this fix, similar to the B3 one?

Done

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.79%. Comparing base (12ee8db) to head (24bd52f).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2604   +/-   ##
=======================================
  Coverage   90.78%   90.79%           
=======================================
  Files         169      169           
  Lines        8056     8059    +3     
  Branches     1643     1645    +2     
=======================================
+ Hits         7314     7317    +3     
  Misses        742      742           

Files with missing lines	Coverage Δ
...ators/propagator-aws-xray/src/AWSXRayPropagator.ts	100.00% <100.00%> (ø)