Allow to isolate Process Groups

[johscheuer]

What would you like to be added/changed?

In some cases it could be beneficial to be able to isolate a set of process groups. The idea of isolation is, that the fdbserver process gets shutdown, but the Pod and the according PVC will be kept running. The isolated process group will not be touched by the operator, that means the operator will not replace or delete those resources until the isolation is removed. This could be a helpful feature to debug a different set of issues, like networking, disk issues or other issues that requires some manual debugging in a Pod. The operator will not use this isolation mechanism automatically and is a feature that could be used by a human operator.