(enhancement) pull in container metadata (-L entries)

[icscript]

It would be extremely helpful to be able to pull in container metadata. For example, the depreciated Container Exporter had a feature where container metadata could be pulled in by specifying "-labels=label1,label2,label3" in the docker run command for the Container Exporter container. This would effectively cause Container Exporter to pull the meta data in from labels that were applied to a monitored container via specifying -L label=value in the monitored containers docker run command.
It would be helpful to have a similar feature for docker exporter where it can bring in monitored containers metadata. Ultimately I'm trying to pull container metadata into prometheus so that alert manager can alert differently based on container metadata. For example I may have a label that indicates whether a container is in production or standby, and hence alerting would occur differently based on this label, but the only way to get a label into prometheus/alertmanager is via something that can pull it from the container such as Container Exporter or hopefully Docker Exporter.