chore(tracing): Adds trace_remote field to TraceDigest

[mabdinur]

What does this PR do?

Adds a mechanism to track whether a TraceDigest represents a remote span or if it is local to a host. This change is analogous to a change made in NodeJS: https://github.com/DataDog/dd-trace-js/pull/4153.

is_remote or trace_remote is an opentelemetry concept and is defined here: https://opentelemetry.io/docs/specs/otel/trace/api/#isremote.

Motivation:

This new field will be used to propagate the last datadog parent id in w3c tracecontext headers. This change blocks: https://github.com/DataDog/dd-trace-rb/pull/3488

Additional Notes:

How to test the 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!

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.07%. Comparing base (344441e) to head (dd684ac).

Additional details and impacted files

@@           Coverage Diff           @@
##              2.0    #3516   +/-   ##
=======================================
  Coverage   98.07%   98.07%           
=======================================
  Files        1237     1237           
  Lines       72254    72276   +22     
  Branches     3408     3408           
=======================================
+ Hits        70863    70886   +23     
+ Misses       1391     1390    -1     

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