Use environment variable and default to PHP's sendmail_path

[joelpittet]

Use sendmail_path in PHP instead of hardcoded path and options

Description

We use mailhog in our DDEV local development with sendmail and in staging we change the sendmail enviroment variable to dump email in the garbage (/tmp).

Instead of using a hardcoded path and options for the sendmail command you can use an environment variable and default to another environment variable provided by PHP.

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

We use this configuration to capture emails in local dev and staging.

Test Configuration:

• PHP version: 8.1
• MySQL version: 8.0
• Webserver version: Apache 2.4
• OS version: Ubuntu/Redhat/macOS

Checklist:

• I have read the Contributing documentation available here: https://snipe-it.readme.io/docs/contributing-overview
• I have formatted this PR according to the project guidelines: https://snipe-it.readme.io/docs/contributing-overview#pull-request-guidelines
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[what-the-diff]

PR Summary

• Updated sendmail path
  The sendmail path has been changed to retrieve its value from the environment variable SENDMAIL_PATH or fall back to the sendmail_path value in the PHP configuration file (php.ini). This improves flexibility in configuring the email sending process.