created adjacency list for recipie and ingredient

- Added pl/PGSQL functions for finding pairs that are connected
- Added tables for each adjacency list (RecipeConnection &
  IngredientConnection)
- Added table to keep track of recipes that have not been merged into
  the graph yet
- Added function to update adjacency list with new recipes

docker/psql/init.sql

@@ -1 +1,42 @@
-CREATE EXTENSION plpython3u
+CREATE EXTENSION plpython3u;
+
+DROP FUNCTION text_pairs;
+CREATE OR REPLACE FUNCTION text_pairs(list TEXT[])
+RETURNS SETOF TEXT[]
+LANGUAGE plpgsql AS
+$$
+DECLARE
+    x TEXT;
+    y TEXT;
+BEGIN
+    for x, y in(
+        SELECT *
+        FROM unnest(list) a 
+        CROSS JOIN unnest(list) b 
+        WHERE a > b)
+    LOOP
+        RETURN NEXT ARRAY [x, y];
+    END LOOP;
+END;
+$$;
+
+
+DROP FUNCTION int_pairs;
+CREATE OR REPLACE FUNCTION int_pairs(list INTEGER[])
+RETURNS SETOF INTEGER[]
+LANGUAGE plpgsql AS
+$$
+DECLARE
+    x INTEGER;
+    y INTEGER;
+BEGIN
+    for x, y in(
+        SELECT *
+        FROM unnest(list) a
+        CROSS JOIN unnest(list) b
+        WHERE a > b)
+    LOOP
+        RETURN NEXT ARRAY [x, y];
+    END LOOP;
+END;
+$$;