New sample apps for XR IS-IS operational data

[saalvare]

We just added a couple of sample apps for XR IS-IS operational data (model Cisco-IOS-XR-clns-isis-oper).  They produce output pretty similar to a couple of popular IS-IS show commands that exist in CLI.  Check them out!

"show isis neighbor"

ydk-py-samples/nc-read-oper-clns-isis-20-ydk.py at master · CiscoDevNet/ydk-py-samples · GitHub

ydk-py-samples/nc-read-oper-clns-isis-20-ydk.txt at master · CiscoDevNet/ydk-py-samples · GitHub

"show isis adjacency"

ydk-py-samples/nc-read-oper-clns-isis-22-ydk.py at master · CiscoDevNet/ydk-py-samples · GitHub

ydk-py-samples/nc-read-oper-clns-isis-22-ydk.txt at master · CiscoDevNet/ydk-py-samples · GitHub

With these, we reach 17 sample apps on IS-IS alone.