Change VRF attachment keys to Switch IP

[mdmohan]

Currently a user have to maintain a static data structure in the TF config for the serial numbers of switches used in the fabric.
Getting the mapping via inventory data source is found to be trouble some in the dependency ordering.
Serial numbers are keys for some of these resources and having that dependant on some other resource/data source cause unnecessary disruptions, when something changes in inventory

Hence the ask is to change the keys of VRF attachments from serial to IP

@pritispa fyi