Wait to load turnstile until user interacts with Touchpoints form

[sanason]

For embedded Touchpoints forms, most users who visit the page containing the form will never actually interact with the form. This PR delays triggering all of the Cloudflare Turnstile processing until the user has given some indication that they might try to respond to the Touchpoints form. Two benefits:

1. Avoids the overhead of loading the Turnstile script and running a challenge for most visits to the page containing the form.
2. Prevents noise in our Turnstile analytics. Right now, we're seeing hundreds of thousands of (non-interactive) challenges solved every day for less than 20 form submissions. I'd like to see numbers that only reflect humans (or bots) who have interacted with the form.