Add GHA for staticcheck and address issues

[gab-arrobo]

Tested changes with OnRamp using the replace directive in the amf and smf go modules (Docker images)
The changes in this PR address the issues shown by staticcheck

$ staticcheck ./...
proto/client/gClient.go:38:2: field sst is unused (U1000)
proto/client/gClient.go:39:2: field sd is unused (U1000)
proto/client/gClient.go:143:35: grpc.WithInsecure is deprecated: use WithTransportCredentials and insecure.NewCredentials() instead. Will be supported throughout 1.x.  (SA1019)
proto/client/gClient.go:144:14: grpc.Dial is deprecated: use NewClient instead.  Will be supported throughout 1.x.  (SA1019)
proto/client/gClient.go:219:6: func readConfigInLoop is unused (U1000)
proto/client/gClient.go:222:2: should use for range instead of for { select {} } (S1000)