Metadata per detectors in the scan_info

On top of !3624 (merged) i would like to expose metadata per detectors in the scan_info.

There is 2 things i want to to:

• Merge scan_info/rois inside scan_info/devices
  • That's something i can handle (it's only used by Flint)
• Expose the kind of devices (or more):
  • There is many ways to do that:
    1. Create a new method like get_device_info in each device classes (or in the acq_obj) and ask the devices to provide a normalized info dict.
    2. Provide a set of normalized types (i.e. NexusWriter _device_info_add_ctr) and compute the mapping in bliss.scanning.scan_info
    3. Store the device qualified class name (or the acq_obj qualified class name)

Do you have preferences? @matias.guijarro @denolf @pguillou?

I think we should aim the 1), but in that case i need help to know what to do on BLISS side.

With that we can start to deflate the reserved nexuswriter metadata which is part of the scan_info. What do you think?