fix(otlp-http-exporter): update endpoint to match spec

[svetlanabrennan]

Which problem is this PR solving?

Problem 1:
Spec says that OTEL_EXPORTER_OTLP_ENDPOINT is used for general endpoint so the http exporter doesn't have to check if a path is included in this endpoint. Our current implementation is checking for path in this endpoint.

Fixes #2816

Problem 2:
Spec says that per-signal variables (OTEL_EXPORTER_OTLP_<signal>_ENDPOINT) should add a root path / if the url contains no path part. Our current implementation doesn't check for root path and doesn't add root path.

Short description of the changes

1. Renamed function from appendResourcePathToUrlIfNotPresent to appendResourcePathToUrl and removed logic around checking for path when user provides endpoint via OTEL_EXPORTER_OTLP_ENDPOINT.
2. Added function called appendRootPathToUrlIfNeeded that will append root path / to url if needed.
3. Updated tests around problem 1 above and added new tests for problem 2 above.
4. Added utils unit test for testing appendResourcePathToUrl and appendRootPathToUrlIfNeeded.

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

• Unit Tests

Checklist:

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

[codecov]

Codecov Report

Merging #2895 (294e544) into main (a9c59da) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2895      +/-   ##
==========================================
+ Coverage   92.51%   92.55%   +0.03%     
==========================================
  Files         183      183              
  Lines        6029     6034       +5     
  Branches     1283     1284       +1     
==========================================
+ Hits         5578     5585       +7     
+ Misses        451      449       -2     

Impacted Files	Coverage Δ
...e-otlp-http/src/platform/node/OTLPTraceExporter.ts	100.00% <100.00%> (ø)
...exporter-trace-otlp-proto/src/OTLPTraceExporter.ts	100.00% <100.00%> (ø)
...-otlp-http/src/platform/node/OTLPMetricExporter.ts	100.00% <100.00%> (ø)
...orter-metrics-otlp-proto/src/OTLPMetricExporter.ts	100.00% <100.00%> (ø)
...perimental/packages/otlp-exporter-base/src/util.ts	97.05% <100.00%> (+7.40%)	⬆️

[pichlermarc]

Looks great! 🙂

[pichlermarc]

/easycla