Use CREATE EXTENSION IF NOT EXISTS in V1__init.sql

The user running the migration might not have superuser permissions.
Using IF NOT EXISTS allows a root user to install the extension
manually, and then the migration will succeed as an unprivileged user.

Signed-off-by: Graham <gpe@openrs2.org>

archive/src/main/resources/org/openrs2/archive/migrations/V1__init.sql

@@ -1,5 +1,5 @@
 -- @formatter:off
-CREATE EXTENSION uint;
+CREATE EXTENSION IF NOT EXISTS uint;
 
 CREATE TABLE games (
     id SERIAL PRIMARY KEY NOT NULL,