fix: export context

Solved the `Exported variable 'xxx' has or is using name 'Context' from external module "./node_modules/daf-selective-disclosure/build/graphql" but cannot be named.` error when using the resolver.

packages/daf-selective-disclosure/src/graphql.ts

@@ -3,7 +3,7 @@ import { ActionTypes, ActionSignSdr, SelectiveDisclosureRequest } from './action
 import { findCredentialsForSdr, validatePresentationAgainstSdr } from './helper'
 import { MessageTypes } from './message-handler'
 
-interface Context {
+export interface Context {
   agent: Agent
 }