Define base Compose resources supported by envoy

* ComposeNamespace,
* ComposeModule (+ fields),
* ComposeRecord (+ values),
* RBAC permissions.

compose/types/module_field_options.go

@@ -4,8 +4,9 @@ import (
 	"database/sql/driver"
 	"encoding/json"
 	"fmt"
-	"github.com/pkg/errors"
 	"strconv"
+
+	"github.com/pkg/errors"
 )
 
 type (
@@ -91,6 +92,19 @@ func (opt ModuleFieldOptions) Strings(key string) []string {
 	return nil
 }
 
+// String returns option value for key as single string
+//
+// Invalid, non-existing are returned as empty string ("")
+func (opt ModuleFieldOptions) String(key string) string {
+	if _, has := opt[key]; has {
+		if v, ok := opt[key].(string); ok {
+			return v
+		}
+	}
+
+	return ""
+}
+
 // IsUnique - should value in this field be unique across records?
 func (opt ModuleFieldOptions) IsUnique() bool {
 	return opt.Bool(moduleFieldOptionIsUnique)