Fix prometheus metric name and unit conversion

[aabmass]

[!IMPORTANT]
This is a breaking change. This PR changes the output prometheus metric names, but the API is not changed.

Description

Fixes https://github.com/open-telemetry/opentelemetry-python/issues/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.

• [x] 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?

• [x] No.

Checklist:

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

[jeremydvoss]

This PR appears to be facing the same spelling issue as mine. Every "assertIn" is now marked as incorrect spelling. How do we add words to the dictionary. Is it just the ignore list in .codespellrc?

[lzchen]

This PR appears to be facing the same spelling issue as mine. Every "assertIn" is now marked as incorrect spelling. How do we add words to the dictionary. Is it just the ignore list in .codespellrc?

https://github.com/open-telemetry/opentelemetry-python/pull/3930