Update NGINX section with comments and fixes

[weiliddat]

I've added comments to potentially close #3300. I've mostly added what the directives and options mean in NGINX, and some basic recommendations. I assumed that the target audience does not necessarily know NGINX that well, and more advanced configurations/explanations are out of scope of the sample config.

I've rearranged some of the SSL configs so it's obvious what is needed and what is optional (OCSP stapling for example).

The proxy_pass directive does not need a port if you are using an upstream group. NGINX will also tell you that it's an error.

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[github-actions]

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