Workspace Proxy UI/UX

Redo/facelift the workspace proxy UI. Including how to interact with the feature.

The current UI for workspace proxies lives in the account settings page:

The RFC had a design like this:

The final UI/UX can be up for discussion in this issue.

Interactions

• Select a workspace proxy.
• Users can manually decide what proxy they want to use
• Clear selection and rely on the default
• "Default" has some logic behind the scenes. The default will be the healthy proxy with the lowest latency. User selection overrides the default.
• If a user's selection becomes unhealthy, their option is ignored and the "default" is chosen.

Implementation details

The entire state of the proxy UI is driven by a context. The new UI should rely entirely on these context values.

https://github.com/coder/coder/blob/stevenmasley%2Fproxy_picker/site/src/contexts/ProxyContext.tsx#L14-L24