Request a bridge tells the captcha is wrong in case of 500

I just got some Internal Server Errors while trying to get bridges with Moat.

But the error presented to the user was that the CAPTCHA solution was wrong. I got to know about the real error only by looking at them in the console.

I think we should add a different error (either something generic, or something that says unexpected error, with a placeholder for the real error, so that users can reach out to us and report the error, if that's the case).

Sadly, it seems that there's a bug in bridgedb for which it can get stuck to a broken state (not public, because it has sensible logs, so I don't know the exact details, either).