Create test job using aigateway omnibus configuration and run the vscode extension tests against it

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Follow on from #520658 (closed)

This task is to get the tests running in the monolith pipeline but there may be improvements we need to implement to make this more maintainable:

1. Produce a docker image for the vscode application under test
2. Add configuration to https://gitlab.com/gitlab-org/gitlab-qa to use the docker image