Add customization for name conversion of metrics

[Slach]

compare metrics between

• https://github.com/ClickHouse/clickhouse_exporter
• https://github.com/Altinity/clickhouse-operator/tree/master/cmd/metrics_exporter
• https://clickhouse.tech/docs/en/operations/server-configuration-parameters/settings/#server_configuration_parameters-prometheus

Add availability to custom metrics query

• https://www.percona.com/blog/2020/06/23/extending-percona-monitoring-and-management-for-mysql-innodb-cluster-with-custom-queries/
• https://github.com/percona/mysqld_exporter/blob/master/collector/custom_query.go