docs(deploy): add ASGI Uvicorn + NGINX deployment guide (#1784)

[zarinpy]

Summary of Changes

Add a production-oriented deployment guide for ASGI Falcon apps with Uvicorn
behind NGINX, parallel to the existing NGINX + uWSGI WSGI guide.

• New page: docs/deploy/uvicorn-nginx.rst (separate OS users, venv,
  asgi:app, Uvicorn workers/proxy headers, optional systemd unit,
  NGINX reverse proxy with TLS and WebSocket upgrade headers)
• Update the deploy preamble to cover both WSGI and ASGI
• Cross-link from the install docs and ASGI tutorial
• Add towncrier newsfragment for Deployment Guide: ASGI apps with Uvicorn #1784

Related Issues

Closes #1784

Pull Request Checklist

This is just a reminder about the most common mistakes. Please make sure that you tick all appropriate boxes. Reading our contribution guide at least once will save you a few review cycles!

If an item doesn't apply to your pull request, check it anyway to make it apparent that there's nothing to do.

• Applied changes to both WSGI and ASGI code paths and interfaces (where applicable).
• Added tests for changed code.
• Performed automated tests and code quality checks by running tox.
• Prefixed code comments with GitHub nick and an appropriate prefix.
• Coding style is consistent with the rest of the framework.
• Updated documentation for changed code.
  • Added docstrings for any new classes, functions, or modules.
  • Updated docstrings for any modifications to existing code.
  • Updated both WSGI and ASGI docs (where applicable).
  • Added references to new classes, functions, or modules to the relevant RST file under docs/.
  • Updated all relevant supporting documentation files under docs/.
  • A copyright notice is included at the top of any new modules (using your own name or the name of your organization).
  • Changed/added classes/methods/functions have appropriate versionadded, versionchanged, or deprecated directives.
• Changes (and possible deprecations) have towncrier news fragments under docs/_newsfragments/, with the file name format {issue_number}.{fragment_type}.rst. (Run tox -e docs, and inspect docs/_build/html/changes/ in the browser to ensure it renders correctly.)
• LLM output, if any, has been carefully reviewed and tested by a human developer. (See also: Use of LLMs ("AI").)

If you have any questions to any of the points above, just submit and ask! This checklist is here to help you, not to deter you from contributing!

PR template inspired by the attrs project.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (ea2b14d) to head (a589b44).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2708   +/-   ##
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  Coverage   100.00%   100.00%           
=========================================
  Files           64        64           
  Lines         7990      7990           
  Branches      1106      1106           
=========================================
  Hits          7990      7990           

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[vytas7]

Thanks @zarinpy , and sorry for the somewhat delayed review.

This looks really good and thought through overall. 💯

Although not critical or detracting value from your contribution, but ideally I would like to find a way to reduce the amount of copy-paste vs nginx-uwsgi.rst, especially the "Running your Application as a Different User" section seems to be a carbon copy.

Maybe we could restructure these docs to share the introductory parts, or, if copy-pasting is the desired outcome, maybe we could factor these snippets into separate files, and use "literalinclude"? 🤔

[zarinpy]

Thanks @zarinpy , and sorry for the somewhat delayed review.

This looks really good and thought through overall. 💯

Although not critical or detracting value from your contribution, but ideally I would like to find a way to reduce the amount of copy-paste vs nginx-uwsgi.rst, especially the "Running your Application as a Different User" section seems to be a carbon copy.

Maybe we could restructure these docs to share the introductory parts, or, if copy-pasting is the desired outcome, maybe we could factor these snippets into separate files, and use "literalinclude"? 🤔

thanks a lot for reviewing my commitment, I will definitely spend good time to make a good change to the docs and push.