Fix: error logged on empty OTEL_TRACES_SAMPLER_ARG

[matthewhughes934]

We were noticing errors like:

time=2024-12-18T15:00:02.080Z level=ERROR
source=/go/pkg/mod/go.opentelemetry.io/contrib/samplers/jaegerremote@v0.27.0/sampler_remote_options.go:112 msg="env variable parsing failure" err="argument is not of type '='"

In applications using the Jaeger sampler but had not set the OTEL_TRACES_SAMPLER_ARG environment variable. The issue was:

• os.Getenv would return "" when this var was not set, and
• strings.Split("", ",") would return []string{""}

since "" does not contain = an error is emitted.

[MrAlias]

Overall, this looks good. Thank you for adding tests to cover your issue. The last remaining thing is a changelog entry for the fix your adding needs to be included.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.5%. Comparing base (dee94b1) to head (4eb890c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #6511     +/-   ##
=======================================
- Coverage   68.5%   68.5%   -0.1%     
=======================================
  Files        200     200             
  Lines      16768   16772      +4     
=======================================
+ Hits       11493   11494      +1     
- Misses      4931    4933      +2     
- Partials     344     345      +1     

Files with missing lines	Coverage Δ
samplers/jaegerremote/sampler_remote_options.go	97.2% <100.0%> (-2.8%)	⬇️

... and 1 file with indirect coverage changes

[matthewhughes934]

Overall, this looks good. Thank you for adding tests to cover your issue. The last remaining thing is a changelog entry for the fix your adding needs to be included.

Thanks! Changelog entry added with 4d72fb9