SvelteKit SSE Example

[karimfromjordan]

This PR implements a simple and relatively portable SSE example using SvelteKit and closes #3. It is able to identify individual clients and handle multiple tabs so it should cover the most important use cases. I started with this one instead of websockets because SSE is generally easier to implement, works directly in SvelteKit without a separate server and therefor seems to also be mentioned more often on Discord.