draft: docs: Transfer Unit docs

[JTorreG]

To-do: Transfer pre-2023 news and release notes.

Proposed changes

• Transfer the NGINX Unit documentation to the documentation repository
• Convert the content from sphinx to Hugo

Note: The scope of this PR is to move the existing content and make sure that it renders properly with Hugo's features (and limitations). Updating the content and IA to follow NGINX guidelines is a separate effort outside of scope.

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• If the change involves potentially sensitive changes, I have assessed the possible impact
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• I have updated any relevant documentation (README.md and CHANGELOG.md)
• I have rebased my branch onto main
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[github-actions]

✅ Deploy Preview will be available once build job completes!

Name	Link
😎 Deploy Preview	https://frontdoor-test-docs.nginx.com/previews/docs/171/

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[mjang]

The content seems fine based on a visual "spot check" diff of a few files. (As noted in the description, this change also included a conversion from rST -> Markdown, so normal "diff" tools would not work)

@Jcahilltorre , the build doesn't work. As shown in the screenshot, whenever I build locally (or use the "frontdoor" build at https://frontdoor-test-docs.nginx.com/previews/docs/171/),

And then point to the NGINX Unit card, I get a direct link to https://unit.nginx.org.

• My guess: the link is "hard coded" somewhere.

But then @Jcahilltorre pointed me to https://frontdoor-test-docs.nginx.com/previews/docs/171/nginx-unit

• And I verify that it also works in a local build, at http://localhost:1313/nginx-unit/

Jon, I'm approving. Just make sure the link works from the docs.nginx.com front page after merge.

[mjang]

Based on other discussion in this PR

[thresheek]

I've noticed a few issues with the content.

1. Seems like the intructions in "2. Install the core package and other packages you need" are broken in the converted site over at https://frontdoor-test-docs.nginx.com/previews/docs/171/unit/installation/#installation-precomp-amazon:
   Compared to https://unit.nginx.org/installation/#amazon-linux there's an extra "``` console" part.

2. Copying a command from the step inserts "#" to the paste buffer. E.g. for the following block:
   when you click "Copy", I see # systemctl restart unit # Necessary for Unit to pick up any changes in language module setup in the paste buffer. On the current site, just systemctl restart unit is getting copied to the paste buffer. This renders copy functionality less useful and will result in errors.