Provide "upload license key" for local-driven paid version enabler

[rodber]

This also concerns chevereto/chevereto

Current Docker provisioning for Chevereto paid edition requires users a build step, which significantly damages the distribution of the project as it makes the process slow and time consuming. It goes worse as each consecutive update also requires to re-build.

There's also a common practice in commercial container runtime providers which offer container manager (ui and more stuff) systems where they often limit docker images to those available in public registries, which pushes our user base to the free edition and use the "DOCKER_SERVICING=server" hack to override the container application runtime.

We should keep the "build your own" as advanced option, must push the whole thing to the container registry and manage application access doing a local license check, exactly how BitWarden does which uses key-based signing process to keep all checks offline.