/metrics output incorrect when multiple metrics share the same name

[tjquinno]

Environment Details

• Helidon Version: 1.x, 2.x
• Helidon SE
• JDK version:n/a
• OS:n/a
• Docker version (if applicable):n/a

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Problem Description

There were several related but different problems involving multiple metrics having the same name (which is permitted if they have different tags).

1. The Prometheus/OpenMetrics output mandates that the TYPE for a given metric must appear only once in the output. The ConcurrentGauge and Meter implementations did not honor this requirement.

2. The /metrics/{registry}/{metricName} endpoint returns only a single metric but should return all metrics matching the name, regardless of tags.

Steps to reproduce

Create multiple metrics of the same metric type sharing the same name bug different tags, then access the application's /metrics/{registry}/{metricName} endpoint. The output reports only one metric instance, not all of them. The problems with ConcurrentGauge and Meter appeared when that first issue was corrected.