Added annotation to locate classes that have an entity id type constant

src/main/java/org/fuin/ddd4j/ddd/EntityIdTypeConstant.java

@@ -0,0 +1,22 @@
+package org.fuin.ddd4j.ddd;
+
+import java.lang.annotation.*;
+
+/**
+ * A class that has a public static constant of type {@link EntityType}.
+ * The expected default name of the constant is <b>TYPE</b>.
+ */
+@Documented
+@Target(ElementType.TYPE)
+@Inherited
+@Retention(RetentionPolicy.RUNTIME)
+public @interface EntityIdTypeConstant {
+
+    /**
+     * Returns the name of a public static constant of type {@link EntityType} in the annotated class.
+     *
+     * @return Name of the public static constant.
+     */
+    String value() default "TYPE";
+
+}