Add disclaimer for renaming "facets"

[amanifarooque]

Summary

Because we will be releasing a faceted search interface, we need to rethink how we refer to "facets", meaning segmented views of search content, in our documentation. For now, we are adding a disclaimer that this naming will change in the future.

I've done this by creating a snippet in the featured-accordion.html includes file so we can reuse the text in several places.

You can see this in action in a few pages:

• https://cg-a72b65a7-73f0-4859-a1d7-dc953cf6ade8.sites.pages.cloud.gov/preview/gsa/search-gov-website/faceted-search-renaming/admin-center/display/display-overview.html
• https://cg-a72b65a7-73f0-4859-a1d7-dc953cf6ade8.sites.pages.cloud.gov/preview/gsa/search-gov-website/faceted-search-renaming/admin-center/content/collections.html
• https://cg-a72b65a7-73f0-4859-a1d7-dc953cf6ade8.sites.pages.cloud.gov/preview/gsa/search-gov-website/faceted-search-renaming/admin-center/content/rss.html

PR Checklist

• [x] Test Cloud.gov Pages preview link for your branch for functionality - make sure all links and buttons work, javascript works as intended, and updates display as expected
• [x] Conduct a HemingwayApp review of the content for plain language. Request plain language review in #helpwanted if needed before merging this PR
• [N/A] Conduct a Lighthouse Audit via Chrome Developer Tools. Identify any issues that must be addressed before merging, and fix
• [x] Ensure no non-public information is published in the commit messages

[amanifarooque]

@dawnpm Re-requesting review, I made your suggested changes above.