[Plan Preview] Enable to compare running resources and target manifests #6217
Description
What would you like to be added:
We want to support the plan preview with the diff between actual resources and target manifests, discussed in #5986
At first, we won't pass RunningDeploySource because it's better to compare TargetDeploySource and LiveState.
In the future, we might add RunningDeploySource to GetPlanPreviewRequest or add a new rpc.
Why is this needed:
For users, it would be nice to know what happens after deploying.