Built-in support for Pub/Sub in Blazor WASM

[dotnetspark]

@mkArtakMSFT here are my thoughts. Take a look at this app for example. Click on any country from Cases by Country/Region/Sovereignty table. You'll notice how all other components were updated instantly. Achieve that UX in Blazor WASM today, I won't go as far as say it's almost impossible but rather time-consuming and hacky, or you have to rely on third party components. EventCallBack<T> is a great deal but is not the best candidate for this. Instead a Pub/Sub will give developers the ability to incrementally grow the UI and to subscribe to events as they go. A good starting point was made in this repo