Fix xray trace metadata segment creation

[DarcyRaynerDD]

What does this PR do?

Respects X-Ray sampling decisions, and doesn't attempt to send a subsegment to x-ray when the whole trace has been sampled out.

Motivation

Prevents sending unwanted segments to x-ray.

Testing Guidelines

I've tested this manually, and create a test.

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
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• This PR passes the integration tests (ask a Datadog member to run the tests)