v0.20.8

Fix #	Description
Fixed bug PMM-8849	Fixed panic on nil data
Improvement PMM-8772	DBStats are disabled by default. Adde 'enable' parameter
Fixed bug PMM-8539	cl_role is always "shardsvr" even for configsvr
Fixed bug PMM-8489	Fixed topology labels on mongos
Improvement PMM-7424	Add support for compatible mode for dbStats metric to provide old metrics
Improvement PMM-7116	myState metric always has a value
Improvement PR #344	Documented minimum permissions needed to collect data