refactor: organize plugin to support multiple services (#1)

Co-authored-by: Michael Li <michael.li@hashicorp.com>

internal/errors/error.go

@@ -0,0 +1,23 @@
+package errors
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+)
+
+// InvalidArgumentError returns an grpc invalid argument status error.
+func InvalidArgumentError(msg string, f map[string]string) error {
+	var fieldMsgs []string
+	for field, val := range f {
+		fieldMsgs = append(fieldMsgs, fmt.Sprintf("%s: %s", field, val))
+	}
+	if len(fieldMsgs) > 0 {
+		sort.Strings(fieldMsgs)
+		msg = fmt.Sprintf("%s: [%s]", msg, strings.Join(fieldMsgs, ", "))
+	}
+	return status.Error(codes.InvalidArgument, msg)
+}