feat: Add entity_guid to Agent Control health file

[amychisholm03]

Description

To facilitate establishing relationships between fleet control agent entities and the related APM service that an agent creates, the entity guid will now be part of the health file written out for agent control. Note that this new field MUST be the first entry in the health file.

From the spec:
"| entity_guid | string | The primary entity GUID received in the connect response. This MUST be the first field in the health file |

This format is based on the OpAMP protocol. The entity
GUID is the first field in the file so as not to break the OpAmp compatibility in the remainder of the file.

For a health file written out prior to the entity GUID being available, the agent should include the entity_guid key with an empty value."

How to Test

npm run unit

Related Issues

Closes #3591

[codecov]

Codecov Report

❌ Patch coverage is 42.30769% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.93%. Comparing base (74777d5) to head (0a06886).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/health-reporter.js	47.82%	12 Missing ⚠️
lib/collector/api.js	0.00%	3 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (74777d5) and HEAD (0a06886). Click for more details.

HEAD has 8 uploads less than BASE

Flag	BASE (74777d5)	HEAD (0a06886)
unit-tests-24.x	1	0
unit-tests-20.x	1	0
unit-tests-22.x	1	0
integration-tests-cjs-20.x	1	0
integration-tests-cjs-24.x	1	0
integration-tests-cjs-22.x	1	0
integration-tests-esm-20.x	1	0
versioned-tests-24.x	1	0

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #3594       +/-   ##
===========================================
- Coverage   97.81%   80.93%   -16.88%     
===========================================
  Files         434      424       -10     
  Lines       56941    55768     -1173     
  Branches        1        1               
===========================================
- Hits        55698    45137    -10561     
- Misses       1243    10631     +9388     

Flag	Coverage Δ
integration-tests-cjs-20.x	?
integration-tests-cjs-22.x	?
integration-tests-cjs-24.x	?
integration-tests-esm-20.x	?
unit-tests-20.x	?
unit-tests-22.x	?
unit-tests-24.x	?
versioned-tests-22.x	80.93% <42.30%> (-0.32%)	⬇️
versioned-tests-24.x	?

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