Improve "Configuring a subdomain" section

[vincent-czi]

Current version has two different www subdomain examples, but I think the intention was for second subdomain example to be a non-www case. Looks like it was supposed to be another used as the subdomain in the second example, but instead the domain name was changed instead (www.example.com becoming www.anotherexample.com).

Why:

Closes 20145
See above description. Filed an issue as well here: #20145

What's being changed (if available, include any code snippets, screenshots, or gifs):

Instead of it being www.anotherexample.com as the second subdomain example (a second www example), making it another.example.com so it's a different subdomain.

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Content directory changes

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Source	Preview	Production	What Changed
pages/configuring-a-custom-domain-for-your-github-pages-site/managing-a-custom-domain-for-your-github-pages-site.md	fpt ghec	fpt ghec

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fpt: Free, Pro, Team
ghec: GitHub Enterprise Cloud
ghes: GitHub Enterprise Server
ghae: GitHub AE

[cmwilson21]

@vincent-czi Thanks for opening a PR and an issue! I've edited your post slightly to link the two together.

I'll get this triaged for review! ⚡

[sophietheking]

Hi @vincent-czi 👋 thanks for opening this PR and improving our docs. We really appreciate it! 💖

This looks good to me, so I'll go ahead and get this merged. 🚀

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