Support rolling updates for regional instance group manager

[ishashchuk]

Add support for rolling update functionality for regional IGM:
https://cloud.google.com/compute/docs/instance-groups/updating-managed-instance-groups#updating_a_regional_managed_instance_group

This is a follow up to this closed issue, where similar functionality was implemented to IGM

[ishashchuk]

This issue can be assigned to myself, since we are committed to have this functionality implemented for both rIGM and IGM. Rolling update for IGM has been already merged into master and we are planning to use similar approach for rIGM using the feedback we've received on that MR.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. If you feel I made an error 🤖 🙉 , please reach out to my human friends 👉 [email protected]. Thanks!