[CX] Change Prometheus metric type from Gauge to Counter

The following metrics need their type to be changed from "Gauge" to "Counter" as they are ever-increasing stats (can reset in case of a restart).

• cbas_io_reads_total
• cbas_io_writes_total
• cbas_gc_count_total
• cbas_gc_time_milliseconds_total
• cbas_failed_to_parse_records_count
• cbas_incoming_records_count

Upon the change, the following needs to be tests:

• In case of an upgrade, does this cause any issues for Prometheus where the type of the metric reported was a Gauge and now it is changed into a Counter?
• How do visualization tools (e.g. Grafana) deal with the metric which type has changed?