OTel:Support reserved attribute overrides

[marcotc]

What does this PR do?

This PR adds support for using reserved OpenTelemetry span attributes to override Datadog Span fields.

Normally, OpenTelemetry span attributes are simply converted to Datadog Span tags, but some attributes should change other properties of the Datadog Span:

• "operation.name" => dd_span.name
• "service.name" => dd_span.service
• "resource.name" => dd_span.resource
• "span.type" => dd_span.type
• "analytics.event" => dd_span.set_metric("_dd1.sr.eausr")

How to test the change?

There are unit tests and system-tests for this change.

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!