fix: Use original regex to get container id from cgroup v1 in fallback case

[nr-ahemsath]

Fixes #2256 by adding additional logic to try and parse the container ID out of cgroup v1 data if the newer regex fails to find anything. Includes a new unit test to verify the intended result.

[tippmar-nr]

Looks good!

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.07%. Comparing base (1632adb) to head (06a960e).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2263      +/-   ##
==========================================
- Coverage   81.09%   81.07%   -0.03%     
==========================================
  Files         396      396              
  Lines       24739    24749      +10     
  Branches     2999     2993       -6     
==========================================
+ Hits        20062    20065       +3     
- Misses       3889     3895       +6     
- Partials      788      789       +1     

Files	Coverage Δ
...gent/NewRelic/Agent/Core/Utilization/VendorInfo.cs	83.73% <100.00%> (+0.25%)	⬆️

... and 3 files with indirect coverage changes