Summary:
Added the changes to make pg upgrade check timeout configurable and defaults to 600.
Also, YBA will pick tserver on master leader node if possible else any random tserver in primary cluster.

Test Plan: Tested manually and https://jenkins.dev.yugabyte.com/view/Dev/job/dev-itest-pipeline/1836/console

Reviewers: svarshney, sneelakantan

Reviewed By: sneelakantan

Subscribers: yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D43608