Update www-and-apex-domain-recommendation.md to fix #39087

[theonlypwner]

Why:

Closes: #39087

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

• Add description of redirect from www.example.com to example.com.
• Add description of redirects between www.blog.example.com and blog.example.com.
• Add description of domains beginning with www.www..
• Add description of only being able to configure one of the domains in the pair www.<domain> and <domain>.

Check off the following:

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require an SME review from GitHub staff.
  • I tested this (but already deleted the test repos) and opened the issue based on my test results.
• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing and the changes look good in the review environment.

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Table of review links

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The table shows the files in the content directory that were changed in this pull request. This helps you review your changes on a staging server. Changes to the data directory are not included in this table.

Source	Review	Production	What Changed
pages/configuring-a-custom-domain-for-your-github-pages-site/about-custom-domains-and-github-pages.md	fpt ghec	fpt ghec	from reusable
pages/configuring-a-custom-domain-for-your-github-pages-site/managing-a-custom-domain-for-your-github-pages-site.md	fpt ghec	fpt ghec	from reusable

Key: fpt: Free, Pro, Team; ghec: GitHub Enterprise Cloud; ghes: GitHub Enterprise Server

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[Sharra-writes]

@theonlypwner The Pages team agrees that this clarification is useful, so I'll get it merged once checks are passing.

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