feat: support filtered subscriptions

packages/server/src/api.ts

@@ -28,8 +28,11 @@ class BaseError extends Error {
 }
 
 const createApi = async (runtime: StashRuntime = new StashRuntime()) => {
-  runtime.documents.on('upserted', (document) => {
-    console.log(document);
+  runtime.documents.subscribe({
+    filter: "metadata.foo = 'bar'",
+    fn: (document) => {
+      console.log(document);
+    },
   });
   const app = fastify().withTypeProvider<ZodTypeProvider>();
   app.setValidatorCompiler(validatorCompiler);