Fix missing exports for built-in plugins

Author: dotansimha

.changeset/swift-turkeys-reflect.md

@@ -0,0 +1,5 @@
+---
+'@envelop/core': patch
+---
+
+Fix missing exports for built-in plugins

packages/core/src/index.ts

@@ -3,3 +3,6 @@ export * from './create';
 export * from './plugins/use-logger';
 export * from './plugins/use-timing';
 export * from './plugins/use-schema';
+export * from './plugins/use-error-handler';
+export * from './plugins/use-extend-context';
+export * from './plugins/use-payload-formatter';