Add grpc plugin (#2758)

* Add grpc plugin

* remove stale readmes

server/grpc/error.go

@@ -0,0 +1,42 @@
+package grpc
+
+import (
+	"net/http"
+
+	"go-micro.dev/v5/errors"
+	"google.golang.org/grpc/codes"
+)
+
+func microError(err *errors.Error) codes.Code {
+	switch err {
+	case nil:
+		return codes.OK
+	}
+
+	switch err.Code {
+	case http.StatusOK:
+		return codes.OK
+	case http.StatusBadRequest:
+		return codes.InvalidArgument
+	case http.StatusRequestTimeout:
+		return codes.DeadlineExceeded
+	case http.StatusNotFound:
+		return codes.NotFound
+	case http.StatusConflict:
+		return codes.AlreadyExists
+	case http.StatusForbidden:
+		return codes.PermissionDenied
+	case http.StatusUnauthorized:
+		return codes.Unauthenticated
+	case http.StatusPreconditionFailed:
+		return codes.FailedPrecondition
+	case http.StatusNotImplemented:
+		return codes.Unimplemented
+	case http.StatusInternalServerError:
+		return codes.Internal
+	case http.StatusServiceUnavailable:
+		return codes.Unavailable
+	}
+
+	return codes.Unknown
+}