Enhance Captcha integration

[jh-RLI]

Description of the issue

We get a lot of spam via the OEP contact form. This is especially due to outdated reCAPTCHA technology. There are new sophisticated solutions which seem to be more successful in bot protection.

Ideas of solution

Use something like https://friendlycaptcha.com/de/

Workflow checklist

• I am aware of the workflow in
  CONTRIBUTING.md