Add ccloud exporter config

[vpolikarpov]

Looks like the default list of metrics in ccloud-exporter code is obsolete and incomplete. It lacks these metrics that were added to Confluent Cloud Telemetry after ccloud-exporter development have been stopped:

• io.confluent.kafka.server/consumer_lag_offsets
• io.confluent.kafka.server/cluster_link_mirror_topic_count
• io.confluent.kafka.server/cluster_link_mirror_topic_offset_lag
• io.confluent.kafka.server/cluster_link_mirror_topic_bytes
• io.confluent.kafka.server/cluster_load_percent

This PR adds config file for ccloud-exporter that provides relevant lists of metrics and labels.