fix: link net and http instrumentations correctly

[seemk]

Which problem is this PR solving?

http instrumentation did not activate the context of the outgoing request span before doing the request, thus net instrumentation received the wrong active context.

Context in the callbacks / event emitters is unchanged, i.e. it is the parent context.

Short description of the changes

Examples show an express app receiving an http request which invokes an outbound http request.

Before

After

[codecov]

Codecov Report

Merging #2046 (c73acbd) into main (ed92829) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2046      +/-   ##
==========================================
+ Coverage   92.99%   93.01%   +0.02%     
==========================================
  Files         152      152              
  Lines        5938     5944       +6     
  Branches     1236     1237       +1     
==========================================
+ Hits         5522     5529       +7     
+ Misses        416      415       -1     

Impacted Files	Coverage Δ
...ges/opentelemetry-instrumentation-http/src/http.ts	95.61% <100.00%> (+0.10%)	⬆️
...emetry-core/src/platform/node/RandomIdGenerator.ts	93.75% <0.00%> (+6.25%)	⬆️

[vmarchaud]

lgtm

[johnbley]

Thanks for this; looks like a clean fix to the issue.