Propagate unknown trace flag bits

[XSAM]

resolves #5030

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.2%. Comparing base (ca35244) to head (249603e).

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #5075     +/-   ##
=======================================
- Coverage   83.2%   83.2%   -0.1%     
=======================================
  Files        243     243             
  Lines      15909   15908      -1     
=======================================
- Hits       13246   13245      -1     
  Misses      2375    2375             
  Partials     288     288             

Files	Coverage Δ
propagation/trace_context.go	96.9% <100.0%> (-0.1%)	⬇️

[MrAlias]

Doesn't this violate this:

... [t]he vendor will only parse the trace-flags values supported by this version of this specification and ignore all other values. [...] Vendors will set all unparsed / unknown trace-flags to 0 on outgoing requests.