Update name of css and js files (cache busting)

[colleenmcginnis]

Change the name of the CSS and JS files to force users to download a new file instead of using a cached version of the existing CSS and JS files.

⚠️ IMPORTANT: If you are looking at this PR as an example of how to do this again or elsewhere (👋 future me) make sure you also change the code in #3019.

Here's what we learned throughout the process:

• When we just tried changing the name of the file that is generated (styles.css to styles-v1.css and docs.js to docs-v1.js), both the tests and the build failed, with the following error:

   Parcel didn't make /tmp/parcel/styles-v1.css at lib/ES/Util.pm line 740
  

• When we looked at line 740 in the lib/ES/Util.pm file, we saw that this was right after running the Parcel CLI. We decided to try renaming not only the name of the file to be created and sent to built-docs as static assets, but also renaming the source files (styles.pcss to styles-v1.pcss and index.js and index-v1.js). After making that change, the build succeeded, but we still had three failing tests related to running the docs locally using --open. All three errors were coming from spec/single_book_spec.rb and were related to the fact that it couldn't find the appropriate CSS/JS files to watch and update automatically when developing locally:

  expected status [200] but was [404]
  

• Finally, to address this we found one last reference to docs.js that we missed because the . was escaped because it was in a regular expression (docs\\.js). This was fixed in Fixes failing test #3019 where both the build and the tests passed.

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[bmorelli25]

Failing docs-test is okay.