Aks-engine: Update pause to 1.3.1

[ritazh]

Describe the request
Currently using mcr.microsoft.com/k8s/core/pause:1.2.0. We should move to a more secure 1.3.1 hosted at mcr.microsoft.com/oss/kubernetes/pause:1.3.1.

Explain why AKS Engine needs it

Describe the solution you'd like

Describe alternatives you've considered

Additional context

[ritazh]

cc @jchauncey @sozercan

[ritazh]

@jackfrancis what's the reason for using mcr.microsoft.com/k8s/core/pause instead of mcr.microsoft.com/oss/kubernetes/pause currently?

[jchauncey]

It was the first place pause landed and they switched because of windows support.

[ritazh]

Can we switch to mcr.microsoft.com/oss/kubernetes/pause for 1.3.1 now?

[jchauncey]

Yes we should

[jackfrancis]

FYI Windows is already using pause 1.3.1 from the oss/kubernetes origin

cc @marosset