[Cluster launcher] [Azure] add option for eviction policy in azure VM template

[bthananjeyan]

Why are these changes needed?

This is necessary to give users the option to pick an eviction policy (Delete vs Deallocate) when nodes in the cluster are pre-empted.

This exposes an additional option that can be set in the node_config attribute in the cluster YAML file.

Related issue number

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[bthananjeyan]

@architkulkarni @ericl @hongchaodeng please let me know if you have any feedback on this PR, or if there is someone else who should be assigned to review it. Thanks!

[bthananjeyan]

@architkulkarni @ericl @hongchaodeng bumping this PR in case it was buried. Please let me know if you have any feedback, or if someone else can be assigned to it. I don't have the ability to assign reviewers.