Create a warning banner to say that "this version assumes you generated your app with --strict"

[mansona]

This task is a blocker for merging #2117 because we want to let people know that this version of the docs assumes that they are going to be using GJS/GTS everywhere.

A good suggestion for the message is that we could say "This guide is written assuming you are using GJS in your app. See this page to read more about GJS"

where this page can link to /components/template-tag-format/ and we can update that page to be relevant to the new branch.

note: this needs to use some in-version data to know to show this banner, we only want this to show on certain versions