Support for invisible hCaptcha and floating Altcha

Is your feature request related to a problem? Please describe. I recently learned about invisible captchas, and found out that [hCaptcha supports them]( Implementing it on the embedded form on my website was fairly straightforward and works beautifully! The initial implementation of hCaptcha was clunky, and didn't mesh well with the website design. This option is a lot more seamless. . To implement it, I had to do the following (updated instructions): 1. Add an id attribute to the Listmonk form 2. Add an id attribute to the submit button 3. Add data-callback="onSubmit" and data-size="invisible" attributes to the hcaptcha <div> 4. Add an additional script before the hosted one The final form code lo…