feature #4: add "article in title" on contitution creation

resources/functions/constitution/find_constitution_title_by_id.sql

@@ -0,0 +1,24 @@
+create or replace function find_constitution_title_by_id(in id uuid, out resource json) language plpgsql as
+$$
+declare
+    _id alias for id;
+begin
+    select to_json(t)
+    from (
+        select
+            ti.id,
+            ti.name,
+            ti.rank,
+            array_agg(a order by ait.rank) as articles
+        into resource
+        from title as ti
+        left join article_in_title ait on ti.id = ait.title_id
+        left join article a on ait.article_id = a.id
+        where ti.id = _id
+        group by ti.id
+        order by ti.rank
+    ) as t;
+end;
+$$;
+
+-- drop function if exists find_constitution_title_by_id(uuid, out json);