[#117] rpc: Allow to specify custom gRPC dialer

After grpc upgrade there is no DialContext call.
So connection is not actually established after created.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

rpc/client/call_options.go

@@ -2,13 +2,16 @@ package client
 
 import (
 	"context"
+
+	"google.golang.org/grpc"
 )
 
 // CallOption is a messaging session option within Protobuf RPC.
 type CallOption func(*callParameters)
 
 type callParameters struct {
-	ctx context.Context // nolint:containedctx
+	ctx    context.Context // nolint:containedctx
+	dialer func(context.Context, grpc.ClientConnInterface) error
 }
 
 func defaultCallParameters() *callParameters {
@@ -27,3 +30,11 @@ func WithContext(ctx context.Context) CallOption {
 		prm.ctx = ctx
 	}
 }
+
+// WithContext returns option to specify grpc dialer. If passed, it will be
+// called after the connection is successfully created.
+func WithDialer(dialer func(context.Context, grpc.ClientConnInterface) error) CallOption {
+	return func(prm *callParameters) {
+		prm.dialer = dialer
+	}
+}