Enhancement: Enable VRF binding for gNMI and Telemetry

[spandan-nexthop]

Note:

This is a copy of sonic-net/sonic-buildimage#23865
Creating the issue specifically in sonic-gnmi for visibility, and because the PR with the sonic-gnmi changes didn't auto assign to anyone.

Is it platform specific

generic

Importance or Severity

High

Description of the enhancement

Operators would like to have an option for configuring a specific VRF for the gNMI and/or the Telemetry process to be bound to.

Current Behavior

Currently gNMI or Telemetry processes cannot be bound to any VRF. Note that there is a VRF argument, but that is used for binding on the ZMQ server side, and not the gNMI/Telemetry server itself.

Proposed Behavior

Both for gNMI and Telemetry, we should add VRF configs in CONFIG_DB. If configured, gNMI and/or Telemetry should be listening only on the configured VRF.

CC

@sneelam20

[bhouse-nexthop]

Need to handle restart of gnmi in GCU on VRF change:
https://github.com/sonic-net/sonic-utilities/blob/master/generic_config_updater/gcu_services_validator.conf.json
https://github.com/sonic-net/sonic-utilities/blob/master/generic_config_updater/services_validator.py

[bhouse-nexthop]

Rework to not allow arbitrary VRF, only default and mgmt.