WIP: Add websocket browser_redirect_url config option

[philpennock]

If an HTTP(S) request is received without the Upgrade: header, then if this new option is set then we'll assume it's a browser and issue a redirect.

There's no flexibility based upon the passed in URL; this should help with redirecting people to dashboards or other tooling.

There's no documentation and no tests, this should not be merged as-is, the PR exists for people to discuss, or replace with something better.

/cc @nats-io/core