Remove any OpenMetrics metric prefixes immediately during parsing

[ofek]

Motivation

So that all other configuration may reference the trimmed metric name, thus eliminating much confusion for users

Additional Notes

I made this Added rather than Fixed since the legacy version did not do this:

integrations-core/datadog_checks_base/datadog_checks/base/checks/openmetrics/mixins.py

Lines 422 to 432 in 45274b9

	type_override = scraper_config['type_overrides'].get(metric.name)
	if type_override:
	metric.type = type_override
	elif scraper_config['_type_override_patterns']:
	for pattern, new_type in iteritems(scraper_config['_type_override_patterns']):
	if pattern.search(metric.name):
	metric.type = new_type
	break
	if metric.type not in self.METRIC_TYPES:
	continue
	metric.name = self._remove_metric_prefix(metric.name, scraper_config)