Add GET /family/{id}/member/{id_member}

geneit_backend/src/extractors/family_extractor.rs

@@ -18,6 +18,12 @@ impl FamilyInPath {
     }
 }
 
+impl From<FamilyInPath> for Membership {
+    fn from(val: FamilyInPath) -> Self {
+        val.0
+    }
+}
+
 impl Deref for FamilyInPath {
     type Target = Membership;