Feature: publish official docker images

[robert-heinzmann-logmein]

Currently there is no official docker image being published for mtail. A typical use case is running mtail next to an application as a sidecar to parse logs and publish the metrics.

It would be great to just use an upstream docker image that matches each version published and avoid setting up custom build pipelines. As this can be official images, build instructions as well as integrity can be ensured.