docs: rewrite private npm module support

[HonkingGoose]

Changes:

Basically a full rewrite.

Major changes:

• Use ordered lists where possible
• Use present tense and active voice
• Grammar fixes
• Use monospaced font for some filenames
• Rename filename so that it is npm specific

I've tried to clarify some difficult to read text, but this needs a review from the maintainers to verify if the text is correct.

Context:

Helps with #7626.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please tick one)

I have verified these changes via:

• Code inspection only, or
• Newly added unit tests, or
• No new tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[rarkins]

@HonkingGoose I think put a pause on this until after we merge v25, then reassess which changes to keep applying. Thanks

[HonkingGoose]

I've force pushed to current main and basically started over, while keeping some changes from the previous commits but dropping others.

I think this PR is ready for a initial "sanity check" review. I don't know if all the text is up to date with the current behavior in the v25 branch.

[viceice]

I think we should make the initial description more generic and add some manager and registry specific samples at bottom.

[HonkingGoose]

We also discussed this a bit in #9205 (docs: explain better how to lookup private Maven repositories), where @rarkins said:

Can you assess how feasible it would be to make the current private modules doc generic instead of npm-specific, or if we should create a new doc which is generic?

What do you like best @rarkins?

1. Keep npm private module docs, create new generic doc for other private modules.
2. Rework current npm private module doc to be more generic like @viceice is suggesting.

[rarkins]

I looked at this today and was thinking it's easiest to rename this to be npm specific and then start over with a new generic doc I'd write

[HonkingGoose]

I've renamed the file so that it's npm specific. This PR is ready for a review as a npm specific document now.

---

I think it makes sense for @rarkins to create a new PR after this one gets merged, so that we can decide what parts we want to keep in the npm docs, and what we want to move/expand on in the generic docs.

We could copy/paste the Self-hosted hostRules section into that generic doc, and link to it from the npm docs, for example. That way we're not duplicating ourselves. 😄

[viceice]

You should add a new document, otherwise we have broken docs links

[rarkins]

You should add a new document, otherwise we have broken docs links

Done. I'll try to fill this out with high priority after the merge

[renovate-release]

🎉 This PR is included in version 25.3.1 🎉

The release is available on:

• GitHub release
• 25.3.1

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