Add opt to set default grpc scheme to passtrough

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

goKMS/main.go

@@ -43,6 +43,7 @@ import (
 	gnmitargetygot "code.fbi.h-da.de/danet/quant/goKMS/model"
 	"github.com/google/uuid"
 	log "github.com/sirupsen/logrus"
+	"google.golang.org/grpc/resolver"
 	"gopkg.in/yaml.v3"
 )
 
@@ -54,9 +55,17 @@ func main() {
 	certFile := flag.String("certFile", "", "location of the gNMI cert file (overwrites settings in config file)")
 	keyFile := flag.String("keyFile", "", "location of the gNMI key file (overwrites settings in config file)")
 	caFile := flag.String("caFile", "", "location of the gNMI ca file (overwrites settings in config file)")
+	gRPCPassthrough := flag.Bool("grpcPassthrough", true, "set the default resolve scheme for grpc to passthrough, default is true")
 
 	flag.Parse()
 
+	if *gRPCPassthrough {
+		log.Info("Setting gRPC default resolver scheme to passthrough. No DNS queries are being made when doing a gRPC request.")
+		resolver.SetDefaultScheme("passthrough")
+	} else {
+		log.Info("gRPC default resolver scheme is not set to passthrough. This might cause issues with the gRPC connection when no real DNS server is available as each gRPC requests requires a DNS request.")
+	}
+
 	// parse string, this is built-in feature of logrus
 	ll, err := log.ParseLevel(*logLevel)
 	if err != nil {