Enable docker (non swarm) auto discovery

[Foxite]

Docker swarm support is added (#60) and it should work with non-swarm deployments as well, however if you start it with --in-docker-swarm you get this:

time="2022-08-15T17:23:00Z" level=fatal msg="Unable to start docker swarm integration" error="Error response from daemon: This node is not a swarm manager. Use "docker swarm init" or "docker swarm join" to connect this node to swarm and try again."

I suggest adding --in-docker to enable autodiscovery in a plain docker engine deployment.

[n1xx1]

The problem with this is that service discovery using a non-swarm environment is different than the swarm one. It requires to reimplement the discovery code for a list of containers instead of a list of services. I don't think that setting up docker swarm is so difficult (https://dockerswarm.rocks/), but if someone has time it's not that hard to do, most of the labels logic should be reusable.