Support for multiple pipeline groups and multiple pipelines

[lquerel]

Until now, our OTAP DF Engine could only start a single pipeline configuration, even though internally our configuration model is already designed to support multiple pipeline configurations grouped into pipeline groups.

We need to add a new parameter --config or -c, mutually exclusive with --pipeline or -p, which will allow specifying an engine configuration declaring 0 to n pipeline groups, each composed of 0 to m pipeline configurations.