feat(configs): enable gNMI API on all network devices

Enables the gNMI (gRPC Network Management Interface) API across all leaf
and spine switches to allow for telemetry streaming and programmatic
device management.

Configuration details:
- Transport: grpc default
- Provider: eos-native

configs/leaf8.cfg

@@ -3,6 +3,11 @@
 !
 hostname leaf8
 !
+! enable gNMI API
+management api gnmi
+   transport grpc default
+   provider eos-native
+!
 ! admin/admin for ssh access
 username admin privilege 15 role network-admin secret sha512 $6$xQktFrbdeqEhVzLM$.1wOJB25nw2fqYaSXDu6y4mo6AP9hngMCFe2vGDl84hWoz00Q.4unoEBqspNI0HEoRz.OZhdBHqQv12KABf0B0