refactor: updating build

[MStokluska]

Summary

Updating server build for frontpage application

Changes

1. Added Apollo Server
2. Used subscription handlers
3. Edited resolvers to match pubsub requirements
4. Removed subscriptions.js

Frontpage server is a reliable example that showcases all related elements for graphql server:

• Subscriptions
• Queries
• Mutations

It is also the one that is really high in google search.
However, the entire example got outdated. This PR updates this example app to use the latest Apollo stack.

Note: we do not use Federation here yet but we can do that in follow up PR

[wtrocki]

@designatednerd I have tested this with Frontpage-IOS app and it works out of the box after regenerating schema.

A related issue in Apollo-Android: apollographql/apollo-kotlin#1648

[wtrocki]

FYI @martijnwalraven