fix(exporters): use parseHeaders() to ensure header-values are not 'undefined'

[pichlermarc]

Which problem is this PR solving?

When passing an options object like { headers: { foo: undefined } } to the http/json and http/protobuf exporters, the headers will not be validated and that will cause

opentelemetry-js/experimental/packages/otlp-exporter-base/src/platform/node/util.ts

Line 89 in abfe059

req = request(options, (res: http.IncomingMessage) => {

to throw, as we're passing an undefined header value. While this alone will not cause an application crash, trying to access req at

opentelemetry-js/experimental/packages/otlp-exporter-base/src/platform/node/util.ts

Line 62 in abfe059

if (req.destroyed) {

will cause the end-user's application to crash within typically 10s after the first export (when using defaults).

This PR fixes this by sanitizing these headers first using parseHeaders().

Fixes #4541

Type of change

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

[codecov]

Codecov Report

Merging #4540 (418b9e3) into main (1b4999f) will decrease coverage by 0.13%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4540      +/-   ##
==========================================
- Coverage   92.83%   92.71%   -0.13%     
==========================================
  Files         328      327       -1     
  Lines        9481     9455      -26     
  Branches     2031     2031              
==========================================
- Hits         8802     8766      -36     
- Misses        679      689      +10     

Files	Coverage Δ
...ogs-otlp-http/src/platform/node/OTLPLogExporter.ts	100.00% <100.00%> (ø)
...gs-otlp-proto/src/platform/node/OTLPLogExporter.ts	100.00% <100.00%> (ø)
...e-otlp-http/src/platform/node/OTLPTraceExporter.ts	100.00% <100.00%> (ø)
...-otlp-proto/src/platform/node/OTLPTraceExporter.ts	100.00% <100.00%> (ø)
...porter-metrics-otlp-grpc/src/OTLPMetricExporter.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	93.44% <100.00%> (ø)

... and 2 files with indirect coverage changes