the couch_docs_fragmentation is not visible on the /metrics endpoint

Hello Team, 

with yapi kredi, they want to add the metric "couch_docs_fragmentation" in their dashboard from the prometheus endpoint, to supervise it and create alert if the value is over 30%.
But the value is not found, and is calculated with the formula : 
 (kv_ep_db_file_size_bytes - kv_ep_db_data_size_bytes)/ kv_ep_db_file_size_bytes
Is there a plan for next release to be included in the /metrics endpoint ? thank you !