Docs: Fix invalid URL

[nginx-aoife]

Proposed changes

I don't know why this issue wasn't picked up in my earlier scans. But there is another broken URL to fix.

Problem: Link in this doc https://docs.nginx.com/nginx-gateway-fabric/how-to/monitoring/troubleshooting/#logs is invalid. User is directed to a 404.

Solution: Updated link to point to https://docs.nginx.com/nginx-gateway-fabric/how-to/control-plane-configuration/

Testing: n/a

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Closes #ISSUE

Checklist

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• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

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