Added new db migration to set default SteamId to

src/main/resources/db/migration/V4__Add_Valid_SteamId.sql

@@ -0,0 +1,9 @@
+UPDATE users
+SET steam_id = 0
+WHERE steam_id IS NULL;
+
+ALTER TABLE users
+    ALTER COLUMN steam_id SET DEFAULT 0;
+
+ALTER TABLE users
+    ALTER COLUMN steam_id SET NOT NULL;