Opt-in option to emulate metric scopes

[jmartisk]

Scope will be appended as a tag rather than prepended to the metric name.
To be more compatible with the MP Metrics 3.0 TCK, we might actually need to prepend it. It is not yet 100 % clear how we will solve this

[jmartisk]

The current micrometer branch has an option smallrye.metrics.append-scope-tags which controls whether metrics created through the legacy MP Metrics APIs (both programmatic and annotated) will get a scope tag.
Not yet sure whether we want to also allow prepending it to the metric name for Prometheus export.