added IF NOT EXISTS to create and CRUD for each table

backend/database/sql/queries/artists.sql

@@ -0,0 +1,17 @@
+-- name: CreateArtist :one
+INSERT INTO artists (name) VALUES (?)
+RETURNING *;
+
+-- name: GetArtist :one
+SELECT * FROM artists 
+WHERE id = ? LIMIT 1;
+
+-- name: UpdateArtist :exec
+UPDATE artists 
+SET name = ?
+WHERE id =?;
+
+-- name: DeleteArtist :exec
+DELETE FROM artists 
+WHERE id =?;
+