Allow operator to autoscale regionserver cluster

[pidren]

Changes required:

• add CRD as configuration expected count of regions per regionserver. For first iteration of this feature it is fine to expect users to manually set this field rather than operator calculate what is the most optimal number of regions per regionserver.
• as part of reconciliation runs, check:

for each regionserver:
   if any regionserver region count > expected region count:
      scale regionserver 
      rebalance regions

As part of first iteration of this feature we do not have to support scaling down regionserver cluster.