[prometheus]: Stabilize OTLP -> Prometheus Summaries

[johannaojeling]

Fixes #4923

Changes

Stabilizes the conversion of OTLP Summaries into Prometheus Summaries.

• Related issues [prometheus] Stabilize OTLP->Prometheus: Summaries #4923
• Related OTEP(s) #
• Links to the prototypes (when adding or changing features)
• CHANGELOG.md file updated for non-trivial changes
  • For trivial changes, include [chore] in the PR title to skip the changelog check
• Spec compliance matrix updated if necessary
• Declarative config data model is updated if SDK config surface is changed

[ArthurSens]

@johannaojeling, I believe David's suggestion was not so literal that we can just copy and paste it into the spec.

Now we have duplicated information, for example, at the top we say:

- A single `{name}_count` metric denoting the count field of the summary.

And at the bottom, we repeat the same information

 The count is converted to the Summary's count.

My interpretation is that the previous way we documented A single {name}_count... is overly focused on the text exposition format and doesn't apply to other Prometheus protocols, such as Remote Write or future improvements planned on the Prometheus side (prometheus/prometheus#16949).

Could you reword the section to be less specific about text format?

[dashpole]

Ah, sorry. I meant to replace the paragraph above, but seem to have messed up the comment anchor.

[johannaojeling]

Closing this as it is being addressed in #5107