Some usability enhancements for Network Observability CLI.

In `oc netobserv flows`:

1. The tab key moves between the flow table and filter field only.  I don't see a way to go to the Play/Pause button, the "+/-" buttons, or the "Manage columns" button using the keyboard.
2. In the "Manage columns" dialog, there's no obvious way to cancel this operation.  It turns out you can do this by just clicking "Save" without any columns selected.
3. In the "Manage columns" dialog, you have to use the keyboard to enable/disable a column.  It should support clicking the row with a mouse.

In `oc netobserv metrics`:

1. In the "Manage panels" dialog, the Escape key doesn't work to close the dialog.  This is unlike "Manage columns" in `oc netobserv flows`, where it does work.