feat:(instrumentation-http) Capture Synthetic Source Type on Requests

[JacksonWeber]

Short description of the changes

Adds support for marking bot/test traffic as synthetic based on the user-agent header.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Added test to ensure that requests that have the appropriate user-agent header are marked as synthetic.

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.95%. Comparing base (8e50498) to head (40eacaf).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5488   +/-   ##
=======================================
  Coverage   94.95%   94.95%           
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  Files         308      308           
  Lines        7928     7928           
  Branches     1604     1604           
=======================================
  Hits         7528     7528           
  Misses        400      400           

[trentm]

(Aside: Eww. I just had my first data loss with GitHub forms. I had a couple comments in pending review, then the PR was updated with new commits, then I hit the GitHub "refresh" link to update the PR diff and it lost my pending review comments.)