fix(sdk-trace-base): don't load envs top level

[lucacasonato]

Which problem is this PR solving? / Short description of the changes

Right now @opentelemetry/sdk-trace-base loads OTEL_* env vars when it is loaded, regardless of if loadDefaultConfig is ever called. In runtimes with a permission model like Deno, this may cause a bunch of permission prompts right on startup. This PR changes the env vars to all be loaded when loadDefaultConfig is called.

Interestingly, previously only buildSamplerFromEnv used the "global" env vars. For all other options the env vars are re-read on every call to loadDefaultConfig.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

I have tested locally that Deno does not prompt for env vars on startup anymore when @opentelemetry/sdk-trace-base is loaded.

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added N/A
• Documentation has been updated N/A

[pichlermarc]

Looks good, thanks 👍
Please also add an entry in CHANGELOG.md 🙂

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.60%. Comparing base (85dcbc7) to head (ffe6c22).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5233      +/-   ##
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- Coverage   94.60%   94.60%   -0.01%     
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  Files         315      315              
  Lines        8012     8011       -1     
  Branches     1617     1617              
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- Hits         7580     7579       -1     
  Misses        432      432              

Files with missing lines	Coverage Δ
...ackages/opentelemetry-sdk-trace-base/src/config.ts	88.37% <100.00%> (-0.27%)	⬇️