Introduce a config to enable setting normalizer target region count through hbase site.

Currently, we can define NORMALIZER_TARGET_REGION_COUNT in table descriptors. I am thinking of introducing a global property through hbase-site so we don't need to set it at each level but just add the property and that would be considered a default value. If we want to override this value we can always use htable descriptor for selected tables.

priority of configs (priority decreases as we move down)

NORMALIZER_TARGET_REGION_COUNT

hbase.normalizer.target_region_count