chore: update docs for CAPTCHAs

[pcaillaudm]

Related Issue or Design Document

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability.
  If this pull request addresses a security vulnerability,
  I confirm that I got approval (please contact security@ory.sh) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added the necessary documentation within the code base (if appropriate).

Further comments

[CLAassistant]

All committers have signed the CLA.

[christiannwamba]

Good to go!

[vinckr]

Tbh I would prefer for this to be in a dedicated document on how to configure CAPTCHA - since the document you added it to is just talking about concepts of security on a high level and does not provide any instructions on how to configure things.
I think a more appropriate place would be for example under Guides -> Operations.

But I will leave it up to @christiannwamba to decide - if urgent we can also merge it as is and later on move it to a more appropriate place.

[piotrmsc]

when we add support for other providers for captchas I think dedicated document will make a lot of sense, for now it's fine with small update as added.