fix(otlp-exporter): add support for signal-specific env vars

[llc1123]

Which problem is this PR solving?

Make all otlp-related env vars work as expected.

Fixes #3193, #3747, #3748

Short description of the changes

Type of change

Please delete options that are not relevant.

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

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Existing tests

Checklist:

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

[codecov]

Codecov Report

Merging #3771 (4701e04) into main (98e4e82) will decrease coverage by 0.98%.
The diff coverage is 50.00%.

❗ Current head 4701e04 differs from pull request most recent head 14ee0c3. Consider uploading reports for the commit 14ee0c3 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3771      +/-   ##
==========================================
- Coverage   93.47%   92.50%   -0.98%     
==========================================
  Files         293      144     -149     
  Lines        8955     3427    -5528     
  Branches     1853      702    -1151     
==========================================
- Hits         8371     3170    -5201     
+ Misses        584      257     -327     

Impacted Files	Coverage Δ
...perimental/packages/otlp-exporter-base/src/util.ts	81.81% <50.00%> (-11.29%)	⬇️

... and 161 files with indirect coverage changes

[pichlermarc]

FIY I'm currently changing the way we're handling configuration in the exporters as part of fixing #3748

[llc1123]

FIY I'm currently changing the way we're handling configuration in the exporters as part of fixing #3748

OK, I'll see what I can help after that.