kv_ep_mem_low_wat_percent_ratio name changed to kv_ep_mem_low_wat_percent in Morpheus

When making the changes required for MB-61457, the intention was to be backwards compatible and continue to expose the same set of metrics. However, I accidenately renamed kv_ep_mem_low_wat_percent_ratio to kv_ep_mem_low_wat_percent, because I did not account for the suffix introduced by the "unit" field in stat_definitions.json.