fix(prometheus): handle metrics with same name but varying tags.

[fieldju]

The functional test and integration tests attached to this PR proves that micrometer-metrics/micrometer#877 (comment) is no longer true.

I have temporarily copy and pasted the registry PrometheusMeterRegistry class:

I have modified the following the offending method to not throw and error and registry a new entry instead:

armory-observability-plugin/common/src/main/java/io/micrometer/prometheus/MutatedPrometheusMeterRegistry.java

Lines 452 to 463 in 2819e3f

	private MicrometerCollector collectorByName(Meter.Id id) {
	return collectorMap.compute(
	getConventionName(id),
	(name, existingCollector) -> {
	List<String> tagKeys = getConventionTags(id).stream().map(Tag::getKey).collect(toList());
	if (existingCollector != null && existingCollector.getTagKeys().equals(tagKeys)) {
	return existingCollector;
	}
	return new MicrometerCollector(id, config().namingConvention(), prometheusConfig)
	.register(registry);
	});
	}