List query on GraphQL side too

That was very simple.

src/schema.rs

@@ -21,6 +21,10 @@ impl Query {
     fn personById(database: &Database, id: String) -> Option<Person> {
         database.get_person(&id)
     }
+
+    fn people(database: &Database) -> Vec<Person> {
+        database.list_people()
+    }
 }
 
 pub struct Mutations;