[pgAdmin4][Patch]: RM#1462- AJAX request do not get fired second time

Hi

Please find attached patch for the fix:
*Issue:*
This issue is regression of one of the flickering issue of RM#1242.
"Aside from displaying/hiding the spinner, panes should have their content
refreshed until and unless the new data differs from the previous, to
reduce flicker"

*Solution:*
Along with caching the node node, we should also keep track of the previous
node clicked.
Fetch new data iff previous node and current node clicked differs.

Please review.

Thanks,
Surinder Kumar