Add remote notifications at extension startup (Cadence 1.0)

[jribbink]

Instructions

Issue To Be Solved

With Cadence 1.0 changes coming and the need for developer preparation, it feels necessary to include some sort of callout within the VSCode extension that can communicate this information to developers.

(Optional): Suggest A Solution

Create a primitive, generalized notification system that simply uses a JSON file in this GH repository to know whether there are any notifications for the developer.

(Optional): Context

Cadence 1.0 changes need to be well communicated to Cadence developers and this is a good funnel.