Add gdk-qa-*-with-load-balancer jobs to test load balancing

What does this MR do and why?

This MR introduces 2 new jobs to our pipeline. These are copies of existing jobs which run QA tests against a GDK installation that runs in a docker container. These 2 jobs take the existing docker container setup with GDK and reconfigure it to use database load balancing with 2 replicas. These jobs run for any changes to the load balancing code.

At present there is no other automated testing of our load balancing code apart from highly stubbeb unit tests. This has meant that mistakes can make it all the way to GSTG before they are noticed. These QA tests will give us more confidence in our changes to load balancing.

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Before	After

How to set up and validate locally

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Related to #371826 (closed)

Related to #393310