Add proto-buf definitions for php-fpm metrics

[achawla2012]

Proposed changes

Add protobuf definitions for php-fpm metrics along the line of old agent schema

Nginx amplify agent schema for php is currently

{   
    'type': 'phpfpm', 
    'root_uuid': 'cfd5d9d600905761ac7c092ddd7e1a95', 
    'local_id': '185502c3d367a8036dfda481e8421e9ae04f6d1031375496ee7bddd7f0a5534a', 
    'name': 'master', 
    'display_name': 'phpfpm master @ Ubuntu', 
    'cmd': 'php-fpm: master process (/etc/php/7.4/fpm/php-fpm.conf)', 
    'conf_path': '/etc/php/7.4/fpm/php-fpm.conf', 
    'workers': 12, 
    'bin_path': None, 
    'version': None, 
    'version_line': None, 
    'pid': 39620, 
    'agent': '1.8.1-1', 
    'children': [
        {
            'type': 'phpfpm_pool', 
            'root_uuid': 'cfd5d9d600905761ac7c092ddd7e1a95', 
            'local_id': '545a2f0f73e2800411ded3a1b4396e8e08b21dfc900ca364bfd2dda420ad84d4', 
            'name': 'wordpress_site', 
            'display_name': 'phpfpm wordpress_site @ Ubuntu', 
            'parent_local_id': '185502c3d367a8036dfda481e8421e9ae04f6d1031375496ee7bddd7f0a5534a', 
            'listen': '/run/php/php7.4-fpm-wordpress-site.sock', 
            'flisten': '/run/php/php7.4-fpm-wordpress-site.sock', 
            'status_path': '/status', 
            'can_have_children': False, 
            'agent': '1.8.1-1'
        }, 
        {
            'type': 'phpfpm_pool', 
            'root_uuid': 'cfd5d9d600905761ac7c092ddd7e1a95', 
            'local_id': 'f53516fd0b4b4924d63e3391a6ebb0f62428f7036fbe0a9643acca681456a3cf', 
            'name': 'www', 
            'display_name': 'phpfpm www @ Ubuntu', 
            'parent_local_id': '185502c3d367a8036dfda481e8421e9ae04f6d1031375496ee7bddd7f0a5534a', 
            'listen': '/run/php/php7.4-fpm.sock', 
            'flisten': '/run/php/php7.4-fpm.sock', 
            'status_path': '/status', 
            'can_have_children': False, 
            'agent': '1.8.1-1'
        }
    ]
}

Checklist

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• 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

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[ryepup]

LGTM, although I'm still curious if we need three copies of the codebase in this codebase

[codecov-commenter]

Codecov Report

Patch coverage: 50.00% and project coverage change: -0.35% ⚠️

Comparison is base (7c1ada3) 67.19% compared to head (496ccbd) 66.85%.
Report is 9 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #452      +/-   ##
==========================================
- Coverage   67.19%   66.85%   -0.35%     
==========================================
  Files         113      113              
  Lines       12849    12931      +82     
==========================================
+ Hits         8634     8645      +11     
- Misses       3647     3715      +68     
- Partials      568      571       +3     

Files Changed	Coverage Δ
...or/github.com/nginx/agent/sdk/v2/config_helpers.go	64.19% <50.00%> (+0.18%)	⬆️

... and 7 files with indirect coverage changes

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[oliveromahony]

not sure why this is required? This is provided elsewhere in the protos https://github.com/nginx/agent/blob/main/sdk/proto/agent.proto#L150

[achawla2012]

I intend to send over agent version only, similar to how old agent schema has.

[oliveromahony]

should the health be separated from the details?

[achawla2012]

I thought of sending it out as part of php-information that will have meta details. Do you have any other thoughts on this?