feature #14: create route for follow article

src/main/kotlin/fr/dcproject/entity/Follow.kt

@@ -0,0 +1,11 @@
+package fr.dcproject.entity
+import fr.postgresjson.entity.EntityI
+import java.util.*
+
+class Follow <T: EntityI<UUID>> (
+    id: UUID = UUID.randomUUID(),
+    citizen: Citizen,
+    override var target: T
+): Extra<T>(id, citizen)
+
+typealias FollowArticleEntity = Follow<Article>