add sql to create library_item_subscriptions db table

packages/db/migrations/0119.do.library_item_subscriptions.sql

@@ -0,0 +1,13 @@
+-- Type: DO
+-- Name: library_item_subscriptions
+-- Description: Create a join table for library item and subscriptions
+
+BEGIN;
+
+CREATE TABLE omnivore.library_item_subscriptions (
+    library_item_id uuid NOT NULL REFERENCES omnivore.library_item(id) ON DELETE CASCADE,
+    subscription_id uuid NOT NULL REFERENCES omnivore.subscriptions(id) ON DELETE CASCADE,
+    PRIMARY KEY (library_item_id, subscription_id)
+);
+
+COMMIT;

packages/db/migrations/0119.undo.library_item_subscriptions.sql

@@ -0,0 +1,9 @@
+-- Type: UNDO
+-- Name: library_item_subscriptions
+-- Description: Create a join table for library item and subscriptions
+
+BEGIN;
+
+DROP TABLE omnivore.library_item_subscriptions;
+
+COMMIT;