refactor(auto-instrumentations-node): migrate away from getEnv()

[pichlermarc]

Which problem is this PR solving?

We're planning to remove getEnv() as it does not scale well when everyone has to update @opentelemetry/core to get their env vars. For OTEL_* there will be a replacement utility function, but until this one is available, we can use process.env directly.

Refs open-telemetry/opentelemetry-js#5443

Short description of the changes

Moves code for parsing OTEL_LOG_LEVEL to @opentelemetry/auto-instrumentations-node here. It may be changed later as we add similar code to @opentelemetry/sdk-node.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.41%. Comparing base (8c56f8d) to head (e96a0a5).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2708      +/-   ##
==========================================
- Coverage   92.45%   92.41%   -0.05%     
==========================================
  Files         171      171              
  Lines        8140     8146       +6     
  Branches     1652     1654       +2     
==========================================
+ Hits         7526     7528       +2     
- Misses        614      618       +4     

Files with missing lines	Coverage Δ
...tapackages/auto-instrumentations-node/src/utils.ts	98.31% <100.00%> (+0.08%)	⬆️

... and 1 file with indirect coverage changes

[trentm]

I'm a little more hesitant on this change, given that this package, sdk-node, and https://github.com/open-telemetry/opentelemetry-lambda/blob/faa6c56645b77d58f170f57ab016e845d815c0a8/nodejs/packages/layer/src/wrapper.ts#L470 would all need this change.

It might still be the easiest transition away from getEnv(), so I'm approving.

[pichlermarc]

I'm a little more hesitant on this change, given that this package, sdk-node, and https://github.com/open-telemetry/opentelemetry-lambda/blob/faa6c56645b77d58f170f57ab016e845d815c0a8/nodejs/packages/layer/src/wrapper.ts#L470 would all need this change.

It might still be the easiest transition away from getEnv(), so I'm approving.

My original draft of the PR in core actually had a utility function to do this. I'll look into adding it back when I open the PR to update @opentelemetry/sdk-node - if there's three places in which this is used, I think there's a good case to add a utility like this. 👍