feat: Create credentials model and graphQL mutation

packages/backend/src/graphql/root-mutation.ts

@@ -0,0 +1,11 @@
+import { GraphQLObjectType } from 'graphql';
+import createCredential from './mutations/create-credential';
+
+const rootMutation = new GraphQLObjectType({
+  name: 'Mutation',
+  fields: {
+    createCredential: createCredential
+  }
+});
+
+export default rootMutation;