Add form processing service integration

[patpluspun]

First step is to find a free/cheap form service that will process forms and send emails to an email address with the form output.

I've used https://formspree.io/ successfully in the past and it's really easy to set up, but the free tier is extremely limited. If anyone has any other options let's hear them.

Integrate the contact form into Apollo's mail handling.

The tricky thing about static sites is there is no underlying web server to hook into mail sending, so we'll need a 3rd party processor to handle emailing form data to where it needs to go.