docs(logs): clarify setTimestamp javadoc for event timestamp behavior

[ruturajjadhav07]

Summary

The Javadoc for LogRecordBuilder#setTimestamp previously stated:

"If unset, it will be set to the current time when emit() is called."

This is incorrect: the implementation only provides a default value for the observed timestamp,
not for the event timestamp.

This PR updates the Javadoc to clarify that:

• Unset event timestamps are NOT automatically populated when emit() is called.
• Only the observed timestamp receives a default value.

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Related Issue

Fixes #8097

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Type of Change

• Documentation update
• Bug fix
• Code change

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: jack-berg / name: Jack Berg (5b0b36a, 794d6ea)
• ✅ login: ruturajjadhav07 / name: Ruturaj Jadhav (317aa33, 5b0b36a, a2b4134)

[jack-berg]

Please apply the note change here as well

[ruturajjadhav07]

Please apply the note change here as well

Updated as suggested. Thank you!

[jkwatson]

Looks like there are some checkstyle problems still.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.35%. Comparing base (0b0929e) to head (794d6ea).
⚠️ Report is 23 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8104      +/-   ##
============================================
+ Coverage     90.32%   90.35%   +0.03%     
- Complexity     7607     7644      +37     
============================================
  Files           839      841       +2     
  Lines         22888    23002     +114     
  Branches       2283     2293      +10     
============================================
+ Hits          20673    20783     +110     
  Misses         1506     1506              
- Partials        709      713       +4     

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[otelbot]

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