Allow to run trivy scans on a worker node

[s4ke]

Currently the design of the exporter only allows to run the scanning on a manager node.

We can change this by:

• Using the tecnativa docker socket proxy for any docker swarm api calls
• A local docker socket for the trivy calls

[s4ke]

The easiest way would be to simply allow to override the url that is used in the DockerClient creation

https://docker-py.readthedocs.io/en/stable/client.html#client-reference

As trivy seems to not have a similar config option