breakout final migration into three different processes

The current final migration has the following:
1. Optional step for quiescing applications

2. Stage migration: migration of PV data and images

3. Migration of all other kube resources except PVC and Image related.

The final migration does all of the above in one shot and in a step-by-step manner. If the user faces problems in step 2, for example, they cannot perform any manual tasks like repairing selected files on PV data and expect the final migration to restore all other kube resources. In order to have a more rounded user experience when PV/image migration is problematic, let's break down the three steps into three different backend API. 

The final migration will still consist of all of these steps, but the UI will call these distinct APIs seperately one after another during the final migration. If one fails, the user can fix it manually and ask users to run the next API from UI continuing migration efforts.

This will allow us to document workaround for restic/velero bugs more effectively providing a list of workaround for known problems.