trace/auto pass stack allocated span context var to ebpf

[RonFed]

same as open-telemetry/opentelemetry-go-instrumentation#1971

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.8%. Comparing base (fabeef0) to head (ccc22b0).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #6434   +/-   ##
=====================================
  Coverage   81.8%   81.8%           
=====================================
  Files        283     283           
  Lines      24927   24928    +1     
=====================================
+ Hits       20401   20404    +3     
+ Misses      4121    4119    -2     
  Partials     405     405           

see 2 files with indirect coverage changes

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