Submit verification code

Submit a verification code for an asset (email OTP, etc.).

Accepted only where the code was delivered out-of-band to the party being verified — an email asset, or a domain challenged over email. A domain asset challenged over dns, http or auto answers 400 unsupported_for_type and completes through POST /api/v1/verify/request/{id}/assets/{assetIndex}/check instead; a phone asset completes when the code reaches us from that number.