chore: Add entity guid to health check file per agent control spec.

[tippmar-nr]

Adds entity guid at the beginning of the health check file as specified by the agent control spec. Includes updated tests.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.39%. Comparing base (9383f42) to head (0b586df).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3284      +/-   ##
==========================================
+ Coverage   82.37%   82.39%   +0.01%     
==========================================
  Files         495      495              
  Lines       31994    31996       +2     
  Branches     3700     3700              
==========================================
+ Hits        26355    26362       +7     
+ Misses       4777     4772       -5     
  Partials      862      862              

Flag	Coverage Δ
Agent	83.63% <100.00%> (+0.01%)	⬆️
Profiler	70.40% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...elic/Agent/Core/AgentHealth/AgentHealthReporter.cs	90.88% <100.00%> (+0.02%)	⬆️
...ent/NewRelic/Agent/Core/AgentHealth/HealthCheck.cs	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.