Draft of an electricStreamToD2Input method

[samwillis]

This is a first draft, and untested.

Used something like:

// Create D2 graph
const graph = new D2({ initialFrontier: 0 })

// Create D2 input
const input = graph.newInput<any>()

// Configure the pipeline
input
  .pipe(
    map(([key, data]) => data.value),
    filter(value => value > 10),
    // ... any other processing / joining
    output((msg) => doSomething(msg))
  )

// Finalize graph
graph.finalize()

// Create Electric stream (example)
const electricStream = new ShapeStream({
  url: 'http://localhost:3000/v1/shape',
  params: {
    table: 'items',
    replica: 'full',  // <-- IMPORTANT!
  }
})

// Connect Electric stream to D2 input
electricStreamToD2Input(electricStream, input)

Addresses #7