Match Accept header with Content-Type in the proto exporter

[scheler]

Which problem is this PR solving?

The protobuf exporter currently sends 'content-type' header as protobuf but 'accept' header as json. Otel collector ignores the accept header and sends the response with protobuf. However, this is an issue with other backends.

Fixes # (issue)

Short description of the changes

Match Accept header with Content-Type in the proto exporter

Type of change

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

How Has This Been Tested?

Tested using the opentelemetry-web example.

[codecov]

Codecov Report

Merging #3562 (33d78aa) into main (9589d54) will decrease coverage by 2.17%.
The diff coverage is n/a.

❗ Current head 33d78aa differs from pull request most recent head 5521fd2. Consider uploading reports for the commit 5521fd2 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3562      +/-   ##
==========================================
- Coverage   93.79%   91.63%   -2.17%     
==========================================
  Files         249      128     -121     
  Lines        7640     3370    -4270     
  Branches     1589      656     -933     
==========================================
- Hits         7166     3088    -4078     
+ Misses        474      282     -192     

Impacted Files	Coverage Δ
api/karma.worker.js	0.00% <0.00%> (-100.00%)	⬇️
api/src/platform/node/globalThis.ts	0.00% <0.00%> (-100.00%)	⬇️
packages/opentelemetry-resources/karma.worker.js	0.00% <0.00%> (-100.00%)	⬇️
...ckages/opentelemetry-sdk-trace-web/karma.worker.js	0.00% <0.00%> (-100.00%)	⬇️
...s/opentelemetry-core/src/platform/node/sdk-info.ts	0.00% <0.00%> (-100.00%)	⬇️
...opentelemetry-core/src/platform/node/globalThis.ts	0.00% <0.00%> (-100.00%)	⬇️
...pentelemetry-core/src/platform/node/performance.ts	0.00% <0.00%> (-100.00%)	⬇️
.../packages/api-logs/src/platform/node/globalThis.ts	0.00% <0.00%> (-100.00%)	⬇️
...lemetry-resources/src/detectors/ProcessDetector.ts	31.81% <0.00%> (-68.19%)	⬇️
...perimental/packages/otlp-exporter-base/src/util.ts	78.04% <0.00%> (-17.08%)	⬇️
... and 126 more

[pichlermarc]

Thank you for fixing this 🙂