Update splunk-otel-javaagent to latest

[srv-gh-o11y-gdi]

Update splunk-otel-javaagent to latest

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 37.90%. Comparing base (c90e56e) to head (10fed15).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6944      +/-   ##
==========================================
- Coverage   37.95%   37.90%   -0.05%     
==========================================
  Files         367      367              
  Lines       25743    25743              
==========================================
- Hits         9770     9758      -12     
- Misses      15161    15169       +8     
- Partials      812      816       +4     

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[Copilot]

Pull Request Overview

This PR updates the Splunk Distribution of OpenTelemetry Java agent from version v2.20.1 to v2.21.1.

• Updates the Java agent version reference from v2.20.1 to v2.21.1
• Adds a changelog entry documenting the update
• Fixes file formatting by removing leading whitespace from the version file

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
instrumentation/packaging/java-agent-release.txt	Updates Java agent version to v2.21.1 and removes leading whitespace to match expected format
.chloggen/update-javaagent.yaml	Adds changelog entry for the Java agent version update with proper issue reference

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