Add warning message when region is unavailable on the controller

[ConnorJC3]

What is this PR about? / Why do we need it?

Adds clearer warning message so customers with cases such as #1357 understand they should manually supply the region.

What testing is done?

N/A

[k8s-ci-robot]

Hi @ConnorJC3. Thanks for your PR.

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[torredil]

/ok-to-test

[torredil]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ConnorJC3, torredil

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