[PHP-FPM] Update the request duration field description in Process data stream

[harnish-crest]

• Bug

What does this PR do?

• Previously we were referring to PHP doc itself, but we found a discrepancy in request duration field. after referring their repo and discussing it with @ManojS-shetty, we are updating the description of it.
• Update the request duration field description.
• Update the visualizations related to the request duration field.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

How to test this PR locally

• Clone integrations repo.
• Install elastic-package locally.
• Start elastic stack using elastic-package.
• Move to (integrations/packages/php_fpm) directory.
• Run the following command to run tests.
  elastic-package test

Related issues

• Relates Create php-fpm package #636
• Relates [PHP-FPM] Add Integration Package with Pool Data Stream #4603
• Relates [PHP-FPM] Add Integration Package with Process Data Stream #4652

[elasticmachine]

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• Start Time: 2022-12-05T12:15:35.202+0000

• Duration: 17 min 31 sec

Test stats 🧪

Test	Results
Failed	0
Passed	12
Skipped	0
Total	12

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[kush-elastic]

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[kush-elastic]

LGTM!

[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (2/2)	💚
Files	100.0% (2/2)	💚 3.0
Classes	100.0% (2/2)	💚 3.0
Methods	100.0% (16/16)	💚 12.903
Lines	95.763% (226/236)	👍 3.83
Conditionals	100.0% (0/0)	💚

[elasticmachine]

Package php_fpm - 0.2.1 containing this change is available at https://epr.elastic.co/search?package=php_fpm