Fix XrayPropagator when no header is present

[khalsah]

This corrects an issue where using XrayPropagator without the x-amzn-trace-id trace header present would cause spans not to get logged/processed.

Background

My use case is in a project that combines tracing, tracing-opentelemetry, opentelemetry, and opentelemetry-jaeger.

I initially had everything working, but when I added the XrayPropagator I noticed that my spans were no longer appearing in jaeger when I made requests directly to my service. I then switched to TraceContextPropagator and everything worked again.

This change simply copies the logic used in TraceContextPropagator into XrayPropagator.

I tested it in my local project and confirmed that with this change traces without a parent are still appearing in jaeger.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: khalsah / name: Hargo Khalsa (db0b14f)

[codecov]

Codecov Report

Merging #867 (db0b14f) into main (c92a1ad) will decrease coverage by 0.0%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            main    #867     +/-   ##
=======================================
- Coverage   66.6%   66.6%   -0.1%     
=======================================
  Files        113     113             
  Lines       8727    8727             
=======================================
- Hits        5820    5813      -7     
- Misses      2907    2914      +7     

Impacted Files	Coverage Δ
opentelemetry-aws/src/lib.rs	89.8% <100.0%> (ø)
opentelemetry-api/src/context.rs	82.9% <0.0%> (-6.0%)	⬇️

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[TommyCpp]

Looks good to me. Good catch

[TommyCpp]

MSRV is probably not related. We will bump to 1.56 before release.