fix(instrumentation-net): make tls span parent of net span

[blumamir]

Which problem is this PR solving?

• In @opentelemetry/instrumentation-net, when tls is used, 2 spans are produced: one for tls and one for network. They are currently siblings to each other and the trace structure does not indicate anything about their relationship, even though they relate to the same tls transaction. In the lack of ambient context (HTTP request span / db driver span) they belong to 2 different traces, as the net span starts in an empty ambient context, thus becomes a root span.

Short description of the changes

• When starting a new tls span, wrap the creation of net span with the tls context so that they are parent-child. Updated the existing tests to assert this behavior

[codecov]

Codecov Report

Merging #1342 (9721bcd) into main (714e6c1) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1342   +/-   ##
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  Coverage   96.08%   96.08%           
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  Files          14       14           
  Lines         893      893           
  Branches      191      191           
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  Hits          858      858           
  Misses         35       35           

[svrnm]

besides the comments from @Flarna it looks good to me!