Support of Exponential histograms in metadatagen

[gizas]

Feature

Description

Add support to the metadatagen tool for the exponential histogram configuration. This will be handled by [Histogram]: aggregation: <explicit|exponential> field that is introduced.

So this generates the config in the metadatagen.
If the user doesn't call Views() and register it with the SDK MeterProvider, the histogram instrument still works — it just falls back to explicit bucket histogram behavior (the SDK default). The exponential aggregation is opt-in at the SDK level, not at the instrument level.

Link to tracking issue

Fixes ##13368

Testing

See the tests added in this PR

Documentation

See cmd/mdatagen/metadata-schema.yaml

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.03%. Comparing base (16076b2) to head (c81fa72).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15057      +/-   ##
==========================================
+ Coverage   91.02%   91.03%   +0.01%     
==========================================
  Files         727      727              
  Lines       48155    48210      +55     
==========================================
+ Hits        43835    43890      +55     
  Misses       3002     3002              
  Partials     1318     1318              

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 3 untouched benchmarks
🗄️ 4 archived benchmarks run¹

---

_{Comparing gizas:exponential_metadata (c81fa72) with main (16076b2)}

Footnotes

1. 4 benchmarks were run, but are now archived. If they were deleted in another branch, consider rebasing to remove them from the report. Instead if they were added back, click here to restore them. ↩

[gizas]

@dmitryax sorry if I rushed with the implementation. From my tests I have seen that only views configuration is the one that gives support of exponential histograms in my setup that is why I followed this approach in this pr.

But lets discuss any ideas and we can change whatever you think

[gizas]

@dmitryax sorry for direct ping here: Any chance you had a look for this ? Let me know if you have any time to discuss the approach

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 14 days.

[gizas]

@dmitryax another ping in order not this to remain stale

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 14 days.

[github-actions]

Closed as inactive. Feel free to reopen if this PR is still being worked on.

[dmitryax]

@gizas sorry for not replying earlier. Are you still interested? If so, I can review after rebase

[gizas]

@dmitryax thank you! I rebased. Sure if you think is valuable it can be of some use for us