[pgAdmin4][RM#4858] Allow user to reconnect to DB server whenconnection is drop

Hi,

Upon downloading the csv file, we used the prompt for re-connecting to the database server when there is a database server connection issue. Currently the user tries to download CSV and there is a connection issue then it is showing a python exception error.

Steps:

1) Open query tool

2) Execute -> SELECT 1,2,3

3) Disconnect from server from browser tree

4) Click on Download CSV button

Current: Python exception error

Expected: It should display dialog to reconnect the server.