[Backport] FTS metrics reported for both _prometheusMetrics and _prometheusMetricsHigh

It appears most/all of the metrics reported by FTS for _prometheusMetricsHigh are also reported for _prometheusMetrics. There shouldn't be anything in common as the ns_server /metrics endpoint returns the combination of both.

To reproduce

• started 3 node cluster_run cluster with all services
• xcurl localhost:9200/_prometheusMetrics
• xcurl localhost:9200/_prometheusMetricsHigh
• compare the results of the above two endpoint. There shouldn't be any duplicates