Update Prometheus spec based on new updates in upstream Prometheus

[ywwg]

Prometheus updated its data model to allow for, among other things, widen the restrictions for allowable metric and label names.

The corresponding specification for Prometheus in this Open Telemetry specification should be updated to match. Specifically, I'd like to make it clear that exporters can optionally pass through Otel names untranslated, with dot separators and no suffixes, to Prometheus. If there are any other differences between the two specifications those should be resolved at the same time.

Tasks:

• Translation strategies from Otel to Prometheus (underscores with suffixes, underscores without suffixes, utf-8 with suffixes, utf-8 without suffixes ("no-translation")
• UTF-8 character support
• Transformation of Exponential and Explicit Histograms into Native Histograms.
• Support histogram NaNs
• Switch from otel_scope_info metric to labels

[cijothomas]

Related: #4371 (comment)

[jpkrohling]

cc @open-telemetry/prometheus-interoperability

[ywwg]

Updating this bug to make it a tracking bug