Support Trace Context extraction from Lambda Context object, and respect user-configured OTEL_PROPAGATORS (#1191)

*Issue #, if available:*
- In latest `com.amazonaws:aws-lambda-java-core:1.4.0`, Lambda Context
has a new `lambdaContext.getXrayTraceId()` method. We need to use this
over SystemProperty/EnvVar to support multi-concurrency in Lambda.

*Description of changes:*
- respect OTEL_PROPAGATORS Env Var priority
  - Priority logic BEFORE:
- Create `carrierA` to contain headers from Lambda request http headers
and the custom client context
- get X-Ray Trace ID from (in order or priority) SystemProperty or
EnvVar, add it to new `carrierB`
- Use Global Propagator to extract trace context from `carrierB` (trace
extraction only works if xray propagator is configured)
- If above trace extraction results in a context that is not
valid&sampled, try again with Global Propagator using `carrierA`
  - Priority logic AFTER:
- Create `carrierA` to contain headers from Lambda request http headers
and the custom client context
- get X-Ray Trace ID from (in order or priority) Lambda Context,
SystemProperty, or EnvVar, add it to `carrierA` (will overwrite x-ray
header value if present from Lambda request http headers).
    - Use Global Propagator to extract trace context from `carrierA`

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

Author: jj22ee

CHANGELOG.md

@@ -12,3 +12,8 @@ For any change that affects end users of this package, please add an entry under
 If your change does not need a CHANGELOG entry, add the "skip changelog" label to your PR.
 
 ## Unreleased
+
+### Enhancements
+
+- Support X-Ray Trace Id extraction from Lambda Context object, and respect user-configured OTEL_PROPAGATORS in AWS Lamdba instrumentation
+  ([#1191](https://github.com/aws-observability/aws-otel-java-instrumentation/pull/1191))

lambda-layer/otel-instrument

@@ -2,7 +2,7 @@
 
 export OTEL_INSTRUMENTATION_AWS_SDK_EXPERIMENTAL_SPAN_ATTRIBUTES=true
 
-export OTEL_PROPAGATORS="${OTEL_PROPAGATORS:-baggage,xray,tracecontext}"
+export OTEL_PROPAGATORS="${OTEL_PROPAGATORS:-baggage,tracecontext,xray}"
 
 export OTEL_SERVICE_NAME=${OTEL_SERVICE_NAME:-${AWS_LAMBDA_FUNCTION_NAME}}