added IF NOT EXISTS to create and CRUD for each table

backend/database/sql/queries/cover_art.sql

@@ -0,0 +1,17 @@
+-- name: CreateCoverArt :one
+INSERT INTO cover_art (is_embedded, file_path, file_type_id) VALUES (?, ?, ?)
+RETURNING *;
+
+-- name: GetCoverArt :one
+SELECT * FROM cover_art 
+WHERE id = ? LIMIT 1;
+
+-- name: UpdateCoverArt :exec
+UPDATE cover_art 
+SET is_embedded = ?, file_path = ?, file_type_id = ?
+WHERE id =?;
+
+-- name: DeleteCoverArt :exec
+DELETE FROM cover_art 
+WHERE id =?;
+