Updated CS example

[JeanLucPons]

This PR update example/ControlSystem/tango.

It shows how a BPM or DeviceAccess can be accessed.
It is similar here to a dynamic catalog in pyaml-cs-oa or tango-pyaml.

from pyaml.accelerator import Accelerator

sr = Accelerator.load("config.yaml")

# print the BPM position
bpm = sr.live.get_bpm("BPM_C01-01") # bpm is a BPM
print(bpm.positions.get())

# Direct access to control system
da = sr.live.get_device("srdiag/bpm/c01-01/SA_HPosition") # da is a DeviceAccess
print(f"h={da.get()} {da.unit()}")

[ubuntu20acu.pons] > python main.py 
[-1.05921952e-05  3.91472705e-06]
h=-1.0592195175840235e-05 m

[TeresiaOlsson]

I find that maybe the name get_device is a bit confusing because many users think device == element. Maybe it can be called get_deviceaccess to make it clearer what it is you will get or you think that name is too long?

[JeanLucPons]

ok we can rename to get_device_access().
@gupichon-soleil what do you think ?
It will impact backends.

[gupichon]

Yes, get_device_access() is ok. The change is minor.