feat: add user role support to database and queries;

fix: add max length validation for refresh token in RefreshRequest;
refactor: use named constants for cache durations in AuthService;
refactor: select all user columns in GetValidUserByLoginCredentials query;

sqlc/schema.sql

@@ -24,6 +24,7 @@ CREATE TABLE IF NOT EXISTS "users" (
   username VARCHAR(20) UNIQUE NOT NULL,
   verified BOOLEAN DEFAULT FALSE,
   registration_date TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  role INTEGER NOT NULL DEFAULT 0,
   deleted BOOLEAN DEFAULT FALSE
 );