Upgrade Rails to 7

[mogul]

I got 24 failing tests without changing any defaults yet.

I'm attempting to replace UJS with turbo-rails but have not had any luck with that yet.

[mogul]

I'm stuck on this problem where importmaps may not work with certain extensions installed.

In particular I see in the browser console:

An import map is added after module script load was triggered.localhost/:1 
Uncaught TypeError: Failed to resolve module specifier "application". Relative references must start with either "/", "./", or "../". localhost/:1 
Uncaught TypeError: Failed to resolve module specifier "list.js". Relative references must start with either "/", "./", or "../".

If I load the page in an Incognito window, I don't see the error. However, I can't find any extensions installed that might interfere.

[mogul]

When submitting (directly, or via the tests) the result is often a 406 with ActionController::UnknownFormat. This appears to be because the search_controller.rb is not set up to respond with HTML.

[rahearn]

Closing in favor of #737