Hard to automate configuration of WGE when running the upgrade command

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Have to customise the ConfigMap object in the PR/repo yourself, which is a bit of code to read and update.

Possible solutions in order of impl. difficulty (ascending).

• gitops upgrade --config-map extra-config (easy, pctl supports this itself)
• gitops upgrade --values values.yaml (read and create configmap)
• gitops upgrade --set "ingress.port.type=NodePort (read and create configmap)

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--set now supported in new upgrade command weaveworks/weave-gitops#1069