Add the ability to display a cluster "name" on the Dashboard status page

If you are launching different Dask clusters and viewing the cluster information in a dashboard it can be hard to correlate a given dashboard to a job.

It would be great to be able to display a custom string _somewhere_ on the dashboard to identify this. For example we currently hard-code the title of the scheduler status page to `Dask: Status` here (https://github.com/dask/distributed/blob/8d0df89be3a33875513199152d23bed220dc91cb/distributed/dashboard/components/scheduler.py#L3488). Being able to add a custom prefix or suffix would help, or alternatively display a panel below the navigation toolbar.