Stop using "any" as propagator generic

[matthieusieben]

The current implementation of the http instrumentation incorrectly assumes that a request headers is always an object. However, NodeJS also allows using an array of strings as request.headers.

The any generic of the propagator classes hides the typing error this should normally generate:

This PR fixes several things:

1. It changes the typing of the propagation utilities to not rely on any as it may cause invisible issues
2. It fixes the injection of propagation headers when the request options is an array
3. It accounts for the fact that header names are case insensitive when setting propagation headers.

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[codecov]

Codecov Report

❌ Patch coverage is 94.59459% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.07%. Comparing base (e6a5776) to head (abe9b70).
⚠️ Report is 32 commits behind head on main.

Files with missing lines	Patch %	Lines
...es/opentelemetry-instrumentation-http/src/utils.ts	91.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6903      +/-   ##
==========================================
- Coverage   95.08%   95.07%   -0.01%     
==========================================
  Files         394      394              
  Lines       13997    14016      +19     
  Branches     3224     3227       +3     
==========================================
+ Hits        13309    13326      +17     
- Misses        688      690       +2     

Files with missing lines	Coverage Δ
api/src/api/propagation.ts	100.00% <100.00%> (ø)
api/src/propagation/TextMapPropagator.ts	14.28% <100.00%> (ø)
...s/opentelemetry-instrumentation-fetch/src/fetch.ts	83.17% <100.00%> (ø)
...ges/opentelemetry-instrumentation-http/src/http.ts	93.41% <100.00%> (-0.08%)	⬇️
...emetry-instrumentation-xml-http-request/src/xhr.ts	93.22% <100.00%> (ø)
...entelemetry-propagator-b3/src/B3MultiPropagator.ts	100.00% <100.00%> (ø)
...es/opentelemetry-propagator-b3/src/B3Propagator.ts	100.00% <100.00%> (ø)
...ntelemetry-propagator-b3/src/B3SinglePropagator.ts	100.00% <100.00%> (ø)
...es/opentelemetry-instrumentation-http/src/utils.ts	87.15% <91.30%> (+0.28%)	⬆️

... and 1 file with indirect coverage changes

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