[EXPORTER] Support empty arrays in OtlpRecordable attributes

[mbrobbel]

Changes

This PR changes behavior for empty array attribute values in OtlpRecordable. Empty array attribute values did not set the AnyValue field to ArrayValue.

However, following the spec it seems we should forward empty arrays.

https://github.com/open-telemetry/opentelemetry-specification/blob/ce2c5946faa9c961ea01d89c7aed83621865b67b/specification/common/README.md?plain=1#L37-L39

Invoking mutable_array_value() before looping over the values sets the AnyValue variant to ArrayValue regardless of the number of items in the iterator.

[marcalff]

Very clean PR, thanks.

Please expand the unit tests to cover every data types beside std::vector<int64_t>.

This will help to catch bugs if somehow the fix for other alternatives gets lost, with bad merges.

[codecov]

Codecov Report

Merging #2166 (c6dfea7) into main (8b7f9b4) will decrease coverage by 0.02%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2166      +/-   ##
==========================================
- Coverage   87.17%   87.15%   -0.02%     
==========================================
  Files         166      166              
  Lines        4777     4777              
==========================================
- Hits         4164     4163       -1     
- Misses        613      614       +1     

see 1 file with indirect coverage changes

[owent]

LGTM and thanks.

[marcalff]

LGTM, thanks for the fix.