Add bot mitigation to donation form

[vladh]

We're already using Cloudflare, so we could use Cloudflare Turnstile.

This basically involves a Cloudflare-hosted Javascript challenge, which is then verified on the server.

[adsmediatg]

Hi, I can help you solve the problem with captcha. Write to me in my Telegram @sakulchai_place or my mail adsmediatg@gmail.com

[vladh]

We have this figured out now, but thanks for offering.