add Linux package - zrok-access

[qrkourier]

The zrok frontdoor guides users to keep a zrok share backend running with a Linux share or Docker.

Now that personalized frontends are gaining popularity (i.e., running a zrok access private command on a VPS to personalize one's domain name, certs, etc. for a zrok share), it's important to support this with a new Linux package as a counterpart to the zrok-share package.

This relates to reorganizing the Docker private access part of the Docker private share guide: #697