Clarify npm package publishing via CI/CD

What does this MR do?

In 🎫 #451789 (internal) I stumbled over these docs and noted that they are partially incorrect and also seem a bit misguided/duplicated.

I've made the following changes:

• Dropped the entire Authenticating via the `.npmrc` section within Publishing a package via a CI/CD pipeline, and promoted the content of the subsection (level 3 heading) with the same name into the top section (level 2 heading).
  • The dropped section was largely a repeat of the identically named section further above, and didn't really make that much sense in CI/CD context:
  • The remaining content in Publishing a package via a CI/CD pipeline is a CI script that creates a .npmrc file, in a way that would overwrite an existing file – so it didn't make sense to just above tell people to create this file – I'm not sure what the intention here was, but I think it's better to just refer/link to the above section that explains the .npmrc file usage in general
• Fixed the CI script section of the remaining content in Publishing a package via a CI/CD pipeline – it was missing one of the two lines that you need in the resulting .npmrc file, so if with the existing example you would get auth errors
• Renamed the CI job from deploy to publish-npm so it's more descriptive (and less confusion with the stage name being the same)
• Replaced your_project_id and your_domain_name with predefined CI variables – I think these placeholders were just there as the Authenticating via the `.npmrc` section was copied from the more general section above, but if we're in CI context we can just use predefined variables for that
• Moved some more words around to make the resulting new structure work better
• Use "will" instead of "should" in the last sentence

I hope this makes sense, let me know if the changes are unclear

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