Add documentation on running NGINX in debug mode

[bjee19]

Proposed changes

Problem: Added support for running NGINX in debug mode in NGF's CP-DP split which changes the old way to run NGINX in debug mode.

Solution: Update docs to show new way to run NGINX in debug mode.

Testing: Generated documentation using make watch.

Checklist

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• I have read the contributing guidelines
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• I have ensured that documentation content adheres to the style guide
• If the change involves potentially sensitive changes¹, I have assessed the possible impact
• If applicable, I have added tests that prove my fix is effective or that my feature works
• I have ensured that existing tests pass after adding my changes
• If applicable, I have updated README.md and CHANGELOG.md

Footnotes

1. Potentially sensitive changes include anything involving code, personally identify information (PII), live URLs or significant amounts of new or revised documentation. Please refer to our style guide for guidance about placeholder content. ↩

[ADubhlaoich]

LGTM!