Add the ability to remove stale endpoint instances on instances tab

[ramonsmits]

The monitoring view had the ability to dril into a specific endpoint. The endpoint instances listed can grow significantly in elastic environments maken the screen loaded with info.

It would be nice if instances can be hidden via a clickable icon to remove clutter.

At the moment the only way to do this is to restart a monitoring instances as all monitoring state is kept in memory thus discarding any state.

This feature is requested by a customer.