Determine php fpm process status

[achawla2012]

Proposed changes

This change determines status of php-fpm (this would be included as part of php-fpm health check).

Testing

Tested via unit/Shell command

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• I have run make install-tools and have attached any dependency changes to this pull request
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• If applicable, I have updated any relevant documentation (README.md)
• If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13

[netlify]

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Name	Link
🔨 Latest commit	df53dd9
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[codecov-commenter]

Codecov Report

Patch coverage: 72.97% and project coverage change: -0.20% ⚠️

Comparison is base (7c1ada3) 67.19% compared to head (df53dd9) 66.99%.
Report is 4 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #454      +/-   ##
==========================================
- Coverage   67.19%   66.99%   -0.20%     
==========================================
  Files         113      114       +1     
  Lines       12849    12966     +117     
==========================================
+ Hits         8634     8687      +53     
- Misses       3647     3708      +61     
- Partials      568      571       +3     

Files Changed	Coverage Δ
src/core/environment.go	52.03% <ø> (+0.07%)	⬆️
...or/github.com/nginx/agent/sdk/v2/config_helpers.go	64.19% <50.00%> (+0.18%)	⬆️
...rc/extensions/php-fpm-metrics/pkg/phpfpm/status.go	74.28% <74.28%> (ø)

... and 9 files with indirect coverage changes

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[achawla2012]

Closing this as this is ported to #460