Synchronous gauge prototype

[sarafonseca-123]

Description

This PR creates a synchronous gauge instrument, based on opentelemetry-java PR Add experimental synchronous gauge #5506. It aims to give support to synchronous gauge as stated on opentelemetry-specification PR Add synchronous gauge instrument, clarify temporality selection influence on metric point persistence #3540.

Fixes # (issue)
#3363

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

This change was tested with multiple unit tests, that were contributed.
Also, it was locally tested with a simple API in Flask integrating with an OTEL server deployed on Kubernetes, using Python 3.8.

Does This PR Require a Contrib Repo Change?

Answer the following question based on these examples of changes that would require a Contrib Repo Change:

• The OTel specification has changed which prompted this PR to update the method interfaces of opentelemetry-api/ or opentelemetry-sdk/

• The method interfaces of test/util have changed

• Scripts in scripts/ that were copied over to the Contrib repo have changed

• Configuration files that were copied over to the Contrib repo have changed (when consistency between repositories is applicable) such as in

  • pyproject.toml
  • isort.cfg
  • .flake8

• When a new .github/CODEOWNER is added

• Major changes to project information, such as in:

  • README.md
  • CONTRIBUTING.md

• Yes. - Link to PR:

• No.

Checklist:

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

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: sarafonseca-123 / name: sarafonseca (c371543, 2ac9b9e, 91a1265, 1d1836d, 064ce06, 472a98b, 86f615c)
• ✅ login: ocelotl / name: Diego Hurtado (7639544, 50193fb)

[ohaibbq]

These changes seem good to me! 🎉
@ocelotl @lzchen how can I help push this PR forward?

[ocelotl]

Well done! ✌️

[agronholm]

What's the status on this? I would very much like to get my hands on the synchronous gauge API.

[agronholm]

@sarafonseca-123 Why did you make Gauge private? Isn't the whole point here to provide that API to end users?

[agronholm]

@sarafonseca-123 Why did you make Gauge private? Isn't the whole point here to provide that API to end users?

Oh, because it's experimental? I only just now saw that in the resolved comments.

[agronholm]

The only thing missing here seems to be one leftover reference in the docs to Gauge that should be _Gauge instead.