Support Auto DevOps with GitLab Kubernetes agent

Auto DevOps is a popular feature but is not currently supported by the Kubernetes agent.

Proposal

Use the CI tunnel to support Auto DevOps

End goal

1. Make it work out of the box. If that is not feasible/reasonable in terms of costs
2. Make it work by setting CI variables.

We can start a first iteration by documenting what variables need to be configured in CI YAML.

Details

Discussion from the team meeting on 2021-10-04

Mikhail Mazurskiy: Is the issue setting Context?
Hordur Yngvason: There are just two things to fix: Setting context and CI variables that are set by GitLab Cluster integration, Kubenamespace, Kubetoken etc
Mikhail Mazurskiy: Docs needed for ADO => Agent?
Hordur Yngvason: Working out of the box would be better
Nicholas Klick: can we just ask them to add a ci.yml?
Mikhail Mazurskiy: Starting with Config as code is a better pattern.
Hordur Yngvason: Users might be concerned about adding a ci.yml
Matt Kasa: Seems like we need to support users that dont want a ci.yml
Mikhail Mazurskiy: ENVs?
Hordur Yngvason: CI vars could work.