Add support for TLS Protect Cloud EU region

[paulternate]

Summary of the new feature/enhancement

Venafi TLS Protect Cloud has recently added support for the EU region and requires an alternate API base URL.

Proposed technical implementation details (optional)

The VCert CLI allows users to pass the -u flag and specify an alternate target URL (instead of the default api.venafi.cloud). It would be great to allow users of this extension to have the option to specify an alternate URL during initial configuration as well.