Add support for custom certificate in the Curl Client

[soarecostin]

Description Added support for setting a custom certificate path in the Curl Client.

This is needed in our scenario when proxying Adyen requests through VGS for PCI compliance.

In addition in this MR, if a proxy URL contains the scheme, the proposed change will keep it in the final URL that gets set into CURLOPT_PROXY. By stripping it, some proxies (VGS included) are not connecting properly.