[pgAdmin4][psycopg2] - Modified status message implementation

Hi,

Please find attached patch file which modified the earlier statusmessage
implementation.

*Previous implementation:- *

statusmessage was implemented inside the poll function and if poll result
row is greater than zero then statusmessage was replaced by the result row
returned so if user wants the statusmessage along with returned rows then
current implementation will not work.

*Changes:-*

Now "status_message()" function is implemented to get the status message
returned by last command executed on the server and removed from the poll
function.
If user wants to status messages then they have to call "status_message()"
which will return the status message text.

Do review it and let us know for any comments.

Thanks,
Neel Patel