Description

Fixes #2938

Updates the prometheus exporter name conversion to match the specification by implementing a few fixes:

• this is a breaking change to prometheus metric names so they comply with the
  specification.
• you can temporarily opt-out of the unit normalization by setting the environment variable
  OTEL_PYTHON_EXPERIMENTAL_DISABLE_PROMETHEUS_UNIT_NORMALIZATION=true
• common unit abbreviations are converted to Prometheus conventions (s -> seconds),
  following the collector's implementation
• consecutive _ are replaced with a single _
• unit annotations (enclosed in curly braces like {requests}) are stripped away
• units with slash are converted e.g. m/s -> meters_per_second.
• The exporter's API is not changed

Type of change

Please delete options that are not relevant.

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

I added a ton of test cases. Many were copied from the collector's test cases. I also added tests for semconv metrics so we can be sure what they will look like.

Does This PR Require a Contrib Repo Change?

• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated