Fix migration resolution path (#10188)

### WHY are these changes introduced?

Fixes a bug with how the migration resolution path is created

### WHAT is this pull request doing?

This update resolves migrations from `<migration-name>/transform.js`

Co-authored-by: Aaron Casanova <32409546+aaronccasanova@users.noreply.github.com>

polaris-migrator/src/migrate.ts

@@ -20,7 +20,7 @@ export async function migrate(
 ) {
   const migrationFile = path.join(
     __dirname,
-    `./migrations/${migration}/${migration}.js`,
+    `./migrations/${migration}/transform.js`,
   );
 
   try {