feat(api-graphql): return entire payload in callback

[iartemiev]

Description of changes

• Include entire subscription message contents in event subscription callback argument.

Given the following incoming subscription message

{
  "id":"ca7ba14c-e71a-45bf-b121-47a578b7c162",
  "type":"data",
  "event":"{\"some\":\"data\"}"
}

Old

channel.subscribe({
  next: (data) => console.log(data);
/*
{ some: "data" }
*/
})

New

channel.subscribe({
  next: (data) => console.log(data);
/*
{
  id: "ca7ba14c-e71a-45bf-b121-47a578b7c162",
  type: "data",
  event: { some: "data" }
}
*/
})

Description of how you validated changes

Checklist

• PR description included
• yarn test passes
• Unit Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)