Ensure all XRay Sampler functionality is under ParentBased logic

[jj22ee]

Description:

This fixes the bug where:

• While the subcomponents of XRay Sampler uses ParentBased logic to short-circuit the Parent's Sampling Decision, the XRay Sampling Statistics recording logic is not skipped when a Parent's Sampling Decision is found. This causes XRay Sampler to produce Sampling Statistics based on number of Spans (regardless of Parent's Sampling Decision), while XRay Sampler should produce Sampling Statistics based on number of Traces (aka the number of root Spans that makes the Sampling Decision)

The changes introduced in this PR are as follows:

• Wrap entire internal XrayRulesSampler of AwsXrayRemoteSampler under a single ParentBased Sampler
• Remove use of redundant ParentBased Sampler logic for internal subcomponents for XRay Sampler.

Existing Issue(s):
Related

• [XRay Sampler] - XRay Sampler Statistics reports much higher RequestCount/SampleCount than expected for Sampling Rules  aws-observability/aws-otel-js-instrumentation#79
• [XRay Sampler] Fix - Ensure all XRay Sampler functionality is under ParentBased logic aws-observability/aws-otel-js-instrumentation#80

Testing:

• Tested Sampler functionality with XRay Sampler test bed - https://github.com/aws-observability/aws-otel-community/tree/master/centralized-sampling-tests
• Added unit test to verify ParentBased sampler is wrapped around XRayRulesSampler.

Documentation:

Outstanding items: