fix: add missing policy directive exports (#2869)

Author: dariuszkuc

.changeset/flat-beans-clap.md

@@ -0,0 +1,6 @@
+---
+"@apollo/federation-internals": patch
+---
+
+Add missing `@policy` directive top level exports
+  

internals-js/src/index.ts

@@ -22,3 +22,4 @@ export { coreFeatureDefinitionIfKnown } from './knownCoreFeatures';
 export * from './argumentCompositionStrategies';
 export * from './specs/authenticatedSpec';
 export * from './specs/requiresScopesSpec';
+export * from './specs/policySpec';