Design document for otelhttpconv package

[dmathieu]

This provides a design document for a new instrumentation, otelhttpconv that would serve as a meta instrumentation for all HTTP packages to more easily share their behavior.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.5%. Comparing base (3ea6585) to head (77d428d).

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #6859     +/-   ##
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- Coverage   75.5%   75.5%   -0.1%     
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  Files        207     207             
  Lines      19319   19319             
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- Hits       14601   14598      -3     
- Misses      4283    4285      +2     
- Partials     435     436      +1     

see 1 file with indirect coverage changes

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[dmathieu]

cc @akats7 @scorpionknifes as code owners of HTTP implementations

[XSAM]

Could you add an example for a certain existing HTTP instrumentation to describe how otelhttpconv is actually being used in HTTP instrumentation? This could also give other authors more clues about how to leverage otelhttpconv to reduce code repetition.

[dmathieu]

I've added a sample implementation of an http.Handler to show what it would look like for implementations.
I'm happy to provide a full implementation of otelhttpconv as well, to make this code work. But I'd rather do that when we're nearing consensus to avoid having to change things too many times.