[mdatagen] bug fix - reaggreagate_set test generation

[jinja2]

Description

Fixes reaggregation test generation when metrics have attributes with requirement_level: required.

1. Config validation failure: The generated testdata/config.yaml included attributes: [] in the reaggregate_set section, but required attributes must always be present. This caused config validation to fail with an error like:

error decoding 'metrics': attributes [required_string_attr] are required for metric reaggregate.metric.with_required

Fix: Updated config.yaml.tmpl to use requiredAttributes helper to include required attributes in the reaggregate_set config instead of an empty array.

2. Test assertion failure: The generated metrics_test.go used different values for required attributes across data points, preventing them from merging during reaggregation. The test expected 1 data point but received 2.

Fix - Updated metrics_test.go.tmpl to use the same value for required attributes across both data points in reaggregation tests, allowing them to merge correctly while still testing that non-required attributes are dropped.

Link to tracking issue

Fixes #

Testing

• Added required_string_attr attribute and reaggregate.metric.with_required metric to samplereceiver/metadata.yaml to cover this scenario

[dmitryax]

LGTM. Thanks Jina!

[codecov]

Codecov Report

❌ Patch coverage is 90.12346% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.80%. Comparing base (ba17669) to head (a8fbbe4).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...plereceiver/internal/metadata/generated_metrics.go	89.18%	8 Missing ⚠️

❌ Your patch status has failed because the patch coverage (90.12%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14441      +/-   ##
==========================================
- Coverage   91.82%   91.80%   -0.03%     
==========================================
  Files         677      677              
  Lines       42610    42677      +67     
==========================================
+ Hits        39128    39179      +51     
- Misses       2423     2436      +13     
- Partials     1059     1062       +3     

☔ View full report in Codecov by Sentry.
📢 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.

[dmitryax]

Actually no need for the changelog given that the feature isn't released yet