Cache Tailscale state for faster startup

[rosszurowski]

Currently when navigating to the Docker extension tab, we need to load the webpage, and then fetch the latest state from Tailscale before we can show anything to users. This means there's usually 300-600ms of loading before anything happens.

I timed it, and it takes 8ms to start up the React page's render, but ~300ms to reach out to the Tailscale service inside the VM. We can trim this down by saving the latest Tailscale state to localStorage so that on subsequent reloads, we have some initial state to show while we revalidate.