initial public release

This is the first public release of our webhook, to integrate cert-manager and Variomedia when it comes to ACME certificate generation.

We've tested this release beforehand, creating "Let's Encrypt" certificates for Kubernetes services in a DNS domain registered with Variomedia.

Major version 2 was selected as a starting point to distinguish against the implementation by jheyduk, which uses a different Variomedia API for the same purpose.