DAG View Improvements

[hari45678]

Tracking the DAG view improvement tasks in this ticket.

• when switched to FDG (of HotROD diagram) the bottom left node was partially covered by the zoom controls. But the chart only allows to zoom in, not zoom out, so no way to make the graph smaller. We should either allocate less space for it or (even better) support zoom out to at least 75%
• The "reload" icon to unset focal service is not very intuitive. Maybe add a Reset button instead. Also allow erasing the depth value
• In the DDG view we have the focal service highlighted with different border. Do something similar for DAG view
• Add an upper limit to the number of nodes that can be viewed without selecting a focal service. Beyond which, force user to select focal service.

[yurishkuro]

Note - I dded it as a sub-issue of the main ticket #2534