Add support for capturing docker id from AWS ECS Fargate.

[jaffinito]

On hold while we wait for more details about the missing linkage with infra.

Description

• Updates GetDockerVendorInfo to check for both the v4 and v3 ECS metadata endpoint URI environment variables and if present parse out the docker from JSON obtain from the endpoint.
• Includes unit tests for both v3 and v4.

Notes:

• Matches docker id captured by the ECS and Docker AWS integrations.
• Environment variables are only read if the CGroup v1 and v2 checks fail (always with ECS Fargate).
• Environment variables are only present in ECS (non-fargate and fargate). No additional web calls will be made outside of that environment.
• Metadata v4 is checked first and if present, v3 will not be used. v3 is a fallback since it will eventually disappear.
• No integration tests since that would either require running in ECS Fargate or faking the environment variables with a fake locally hosted endpoint. The unit test does basically the same thing without the extra effort.

Once/If this is approved, I will update the agent specs with our implementation.

Author Checklist

• [x] Unit tests, Integration tests, and Unbounded tests completed
• [x] Performance testing completed with satisfactory results (if required)

Reviewer Checklist

• [x] Perform code review
• [x] Pull request was adequately tested (new/existing tests, performance tests)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 70.58824% with 15 lines in your changes are missing coverage. Please review.

Project coverage is 80.56%. Comparing base (0be7ccd) to head (fe2a7d1).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2481   +/-   ##
=======================================
  Coverage   80.55%   80.56%           
=======================================
  Files         459      459           
  Lines       28759    28802   +43     
  Branches     3152     3159    +7     
=======================================
+ Hits        23168    23203   +35     
- Misses       4812     4817    +5     
- Partials      779      782    +3     

Flag	Coverage Δ
Agent	81.50% <70.58%> (-0.01%)	:arrow_down:
Profiler	72.15% <ø> (ø)

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

Files	Coverage Δ
...gent/NewRelic/Agent/Core/Utilization/VendorInfo.cs	82.47% <70.58%> (-1.00%)	:arrow_down:

... and 1 file with indirect coverage changes