Switch the GKE apps to use the kas agent

What does this MR do?

For the main GKE ci cluster, we have connected the kas agent. (In addition to still having the old deprecated kubernetes account connection).

This MR switches production gke and review gke apps to use the agent.

The kas agent connection's config is managed in a seperate project over here: https://gitlab.com/gitlab-org/distribution/infrastructure/kube-agents/-/blob/main/.gitlab/agents/gke-ci-cluster/config.yaml (I chose to manage the config in a separate project due to this project being mirrored to dev, but the agents being environment specific.)

The changes include the following:

Setting the kubectl context

• Because during our transition, our jobs have multiple kube contexts available, we need to be sure to switch to the new agent based one.

Setting the KUBE CI variables on the jobs directly

• Things like the namespace and ingress were CI variable settings provided by the old k8s integration, that aren't present with the new one.

Related issues

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened