Add rolesJson to groups table

This will contain the roles ('role definition') of a group of
users. We will internally map these to our API scopes.

migrations/schema.sql

@@ -31,6 +31,7 @@ CREATE TABLE IF NOT EXISTS users(
 CREATE TABLE IF NOT EXISTS groups(
     id VARCHAR(128) NOT NULL UNIQUE,
     name VARCHAR(254) NOT NULL UNIQUE,
+    rolesJson TEXT NOT NULL,
     PRIMARY KEY(id));
 
 CREATE TABLE IF NOT EXISTS groupMembers(