What does this PR do?

The processName function is not UTF-8 aware. It simply cuts the string to a fixed length without checking whether the index falls in the middle of a multibyte sequence, which results in corrupted UTF-8. Fix it by truncating the string using a UTF-8 safe approach.

Why is it important?

Prevents SetupMetricsOptions from erroring out on the call to procStats.Init() when trying to apply a regex on a corrupted utf8 string here. See comment on linked issue for details.

How to test this PR locally?

# should fail on main
git checkout main -- ./report/setup.go
go test -run ^TestProcessName$ ./report -v -count=1

# and work on this PR
git stash
go test -run ^TestProcessName$ ./report -v -count=1

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.md

Related issues

• For [beats receivers] OTel manager failed: error creating metricbeatreceiver: error setting up metrics report: failed to init process stats for agent: failed to compile regexp [User.Name��]: error parsing regexp: invalid UTF-8: �� elastic-agent#11172.