added gNMISubscitptions.txt into gosdnc container
Description
Following error occured:
Error reading in gNMI subscription paths, can not watch network elements automatically: open controller/configs/gNMISubscriptions.txt: no such file or directory.
This is now fixed by copying the gNMISubscriptions.txt file into the gosdn-controller container and modifying the path containerlab-gosdn.toml.example, so that it matches.