captcha: imporve condition checks for cloudflare turnstile

[XiaochenCui]

This PR is a continue of #1129

• Add checks for "enabled" is false.
• Fix checks in the frontend, make signup works when "cloudflare turnstile" turned off. (Tested manually)

The next step is to:

• make the "cloudflare turnstile" widget invisible since the signup window is already crowded
• finish the docs

[XiaochenCui]

@jelveh @ProgrammerIn-wonderland this PR is ready for review/merge

[jelveh]

this is conflicting now. I want to wait until the second part (as mentioned in description) is implemented as well before I go for full review

[XiaochenCui]

this is conflicting now. I want to wait until the second part (as mentioned in description) is implemented as well before I go for full review

Do you mean the invisible widget for captach? I'll open this PR when that's implemented

[XiaochenCui]

now it's ready for review/merge, I set the widget to invisible when verification success