[EXPORTER] ostream log exporter, fix memory ownership issues

[marcalff]

Fixes #3135
Fixes #2651

Changes

Fixed the following memory ownership issues in the ostream log exporter:

• In class ReadWriteLogRecord, member body_ now owns a copy of the log body
• In class ReadWriteLogRecord, member attributes_map_ now owns a copy of log attributes

This prevents the use of stale pointers, that could lead to crashes previously.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.87%. Comparing base (44018b0) to head (064b082).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3417      +/-   ##
==========================================
- Coverage   90.01%   89.87%   -0.13%     
==========================================
  Files         212      212              
  Lines        6932     6936       +4     
==========================================
- Hits         6239     6233       -6     
- Misses        693      703      +10     

Files with missing lines	Coverage Δ
sdk/src/logs/read_write_log_record.cc	96.43% <100.00%> (+0.05%)	⬆️

... and 8 files with indirect coverage changes

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[lalitb]

Nicely done, thanks. I would ideally prefer to get rid of ReadableLogRecord, and just have ReadWriteLogRecord (probably renamed to LogData), and so have the API consistent with SpanData, but that's not related to the issue :)

[ThomsonTan]

Is this a breaking change if ReadWriteLogRecord is used by the user? Mention this in the changelog if so.

[ThomsonTan]

Nicely done, thanks. I would ideally prefer to get rid of ReadableLogRecord, and just have ReadWriteLogRecord (probably renamed to LogData), and so have the API consistent with SpanData, but that's not related to the issue :)

Seems #3147 includes the renaming to LogRecordData.