Add support for reCAPTCHA Enterprise

Reroll against latest dev.

At this point we should be using "v1" instead of the "v1beta1" per the documentation (https://cloud.google.com/recaptcha-enterprise/docs/migration-v1).

If you are using v1beta1 to create and annotate assessments, we recommend using v1because the new features, such as reCAPTCHA Enterprise account defender are available only on v1. v1 supports both API key and service account authentication.

Also the url that's constructed is pointing to the site secret and for enterprise it should be pointing to the site key instead.

Started an MR with the patch applied and the URL targeting v1 - required updating how the score is accessed in the API response.

Also the url that's constructed is pointing to the site secret and for enterprise it should be pointing to the site key instead.

@oheller - can you clarify this?