DQM should be able to handle several NectarCAM cameras

[jlenain]

Please describe the use case that requires this feature.
Currently, the DQM can only handle data aquired with the NectarCAM qualification model, as some tel[0] attributes are hard-coded there.

Describe the solution you'd like
The DQM should be able to dynamically, auto-discover which camera is used based on the data that are read.

Describe alternatives you've considered
Instead of using tel[0] to access telescope data, one could for instance use something like:

tel_id = list(evt.nectarcam.tel.as_dict().keys())[0]
....tel[tel_id]....

Additional context
Such a change should also be reflected in other core classes, which currently use:

__class__.TEL_ID.default_value

which default to 0 for the telescope ID field in NectarCAMComponent attributes. The easiest would be to dynamically read that, with a first loop on the EventSource with max_events=1 and discover the tel_id using the same mechanism. Since these core classes all derive from a given mother class, just one implementation in the __init__ method of said mother class would be enough.