added IF NOT EXISTS to create and CRUD for each table

backend/database/sql/queries/release_groups.sql

@@ -0,0 +1,17 @@
+-- name: CreateReleaseGroup :one
+INSERT INTO release_groups (name) VALUES (?)
+RETURNING *;
+
+-- name: GetReleaseGroup :one
+SELECT * FROM release_groups 
+WHERE id = ? LIMIT 1;
+
+-- name: UpdateReleaseGroup :exec
+UPDATE release_groups 
+SET name = ?
+WHERE id =?;
+
+-- name: DeleteReleaseGroup :exec
+DELETE FROM release_groups 
+WHERE id =?;
+