Load and show recaptcha on homepage on-demand

[devnook]

Extracted from #9409

On the homepage, recaptcha also shows up in the trace of these interactions, tracking attribute changes (like inert) across the whole page with mutation observers. It's not a huge amount of work, but again seems completely unnecessary for this interaction. Should recaptcha be loaded more on demand, maybe once a user starts interacting with the form at the bottom of the page?

We could also load it only when the subscribe form get scrolled into the view.