Install prereqs for new ADO build agents

[mboersma]

Change description

Installs several prerequisites if necessary before building Azure SIG images.

This is needed because the build agents used to build CAPZ ref images were recently updated, but are now more bare-bones.

Related issues

• Fixes #

Additional context

I've tested this in-place on the pipeline and it works.

[k8s-ci-robot]

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[mboersma]

/test pull-azure-sigs

Some kind of auth flake...

[mboersma]

/hold

Need to adjust something during the publishing phase.

[mboersma]

/hold cancel

I had to install azure-cli in the promote and cleanup stages as well.

[k8s-ci-robot]

@mboersma: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-azure-vhds	8fbe52d	link	true	/test pull-azure-vhds
pull-azure-sigs	8fbe52d	link	false	/test pull-azure-sigs

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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