Fixed #8543: Change trustedproxy.php to read env('APP_TRUSTED_PROXIES') again

[fashberg]

• trustedproxy.php sets 'proxies' again according to
  env('APP_TRUSTED_PROXIES') again

Description

copying APP_TRUSTED_PROXIES from ENV to settings has been removed at commit 533649f

Diff:
533649f#diff-65b9650370ce063c0ae4c2d172d40fb6aafd2d2e8fe478dae7da21732d4d36dd

This patch undoes that change so snipe-it can now work in docker again!

Fixes #8543
Closes PR #8556 (master<-master) - here develop<-develop as requested in PR Guide)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Test Configuration: official docker image

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

[welcome]

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