Add missing event timestamps to opentelemetry-stdout

[SkaillZ]

Fixes #1390

Changes

Adds timestamps to events in opentelemetry-stdout.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: SkaillZ / name: Rene B. (0610412)

[cijothomas]

thanks for the PR! Could you go through the easycla process and get it cleared, as it is a mandatory prerequisite for accepting contributions! If you are working on behalf of a company, may be good idea to consult legal team as well.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (3939ab5) 57.2% compared to head (0610412) 57.3%.

Files	Patch %	Lines
opentelemetry-stdout/src/trace/transform.rs	0.0%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #1391   +/-   ##
=====================================
  Coverage   57.2%   57.3%           
=====================================
  Files        146     146           
  Lines      18126   18128    +2     
=====================================
+ Hits       10372   10390   +18     
+ Misses      7754    7738   -16     

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[SkaillZ]

@cijothomas I've signed it.

[cijothomas]

@cijothomas I've signed it.

Thank you!