No-limit Drone server CI pipeline

The official Docker images provided by the Drone CI project use the Enterprise version, which is limied to a total of 5000 builds unless the server is in posession of a valid Enterprise license. For personal or small-company (<$1M yearly revenue) use this limitation can be avoided by compiling the Drone server with the nolimit tag.

This CI pipeline attempts to build the latest version of the Drone server by:

• Cloning the repository from Github
• Checking out the latest version tag
• Parsing the repository's .drone.yml file to determine what Golang image to use
• Compiling with the nolimit tag
• Building the Docker image using the included Dockerfile
• Deploying said dockerfile to a private registry