Updated ECS detector containerID logic

[akats7]

Update the ECS detector to properly extract the containerID from cgroup file.

Resolves #7500

Failing tests in opentelemetry-go-contrib/detectors/aws/ecs/test/ecs_test.go were due to incorrect logic pertaining to cgroup paths on valid ecs containers vs other non empty values

Added tests for extracting containerIDs from various cgroup path values

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@9062a3c). Learn more about missing BASE report.
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
detectors/aws/ecs/ecs.go	87.5%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##             main   #7607   +/-   ##
======================================
  Coverage        ?   78.7%           
======================================
  Files           ?     186           
  Lines           ?   14818           
  Branches        ?       0           
======================================
  Hits            ?   11672           
  Misses          ?    2798           
  Partials        ?     348           

Files with missing lines	Coverage Δ
detectors/aws/ecs/ecs.go	64.8% <87.5%> (ø)

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[flc1125]

Nice