fix(proto): accept omitted and proto-named OTLP JSON collector fields

[bruno-espino]

Changes

The OTLP collector request schemas define their resource arrays as repeated fields. The ProtoJSON mapping omits empty repeated fields by default, and requires parsers to accept both the lowerCamelCase JSON name and the original proto field name. OTLP uses that mapping and says empty telemetry requests should succeed.

The generated collector request types instead require the resource array and only recognize its lowerCamelCase name. For example, an empty logs request ({}) fails with missing field resourceLogs, while a valid resource_logs field is not recognized.

Add serde defaults and proto-name aliases for the trace, log, metric, and profile request roots, and configure the generator to preserve them. Regression tests cover omitted roots and both accepted field-name forms.

This was also tested through an OTLP receiver's JSON ingest path: upstream main rejected {} with missing field resourceLogs; with this change, {} decodes as an empty request and {"resource_logs":[{}]} retains its resource entry.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated
• Appropriate CHANGELOG.md updated
• No public API changes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.2%. Comparing base (0e78170) to head (2d2c504).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3602   +/-   ##
=====================================
  Coverage   83.2%   83.2%           
=====================================
  Files        130     130           
  Lines      28246   28246           
=====================================
  Hits       23506   23506           
  Misses      4740    4740           

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