refactor bats test

[tyler36]

This PR updates the addon's main tests.

Previously, we simple checked if Cypress could report its version number (although we didn't care what it was).

This PR refactors the test to:

• Serve a HTML page via DDEV
• Run cypress to confirm it can load and read the page.

This acts as a "real" test by actually using Cypress and supplying an example use that others can follow.

[tyler36]

rebased