Oversampling Mitigation

[atshaw43]

Issue #, if available:

Description of changes:
Allow customer to override the sampling decision on subsegments.

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

[atshaw43]

Some example functionality

package main

import (
   "context"
   "github.com/aws/aws-lambda-go/events"   
   "github.com/aws/aws-lambda-go/lambda"   
   xrayLambda "github.com/aws/aws-xray-sdk-go/lambda"   
   "github.com/aws/aws-xray-sdk-go/xray"
)

func HandleRequest(ctx context.Context, event events.SQSEvent) (string, error) {
   var toSample = false
   
   for _, message := range event.Records {
      if xrayLambda.IsSampled(message) {
         toSample = true
      }
   }

   if toSample {
      ctx, _ = xray.BeginSubsegment(ctx, "test-lambda-1")
   } else {
      ctx, _ = xray.BeginSubsegmentWithoutSampling(ctx, "test-lambda-2")
   }

   xray.GetSegment(ctx).Close(nil)

   return "Done", nil
}

   func main() {
        lambda.Start(HandleRequest)
   }
}

[willarmiros]

Hmm seems the Lambda test case added is failing, the CI failures may not just be related to concurrency issues: https://github.com/aws/aws-xray-sdk-go/actions/runs/3341004880/jobs/5532097421#step:4:157

[wangzlei]

LGTM