Add the base docker image to w3c context validation tests

[yuktea]

To speed up the test setup, the base docker image is put to use in the docker-compose file for W3C trace-context validation tests .
A part of Issue #589

[codecov]

Codecov Report

Merging #673 (8b96423) into main (4592a27) will increase coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main     #673      +/-   ##
============================================
+ Coverage     85.26%   85.28%   +0.02%     
+ Complexity     1153     1151       -2     
============================================
  Files           128      128              
  Lines          2789     2794       +5     
============================================
+ Hits           2378     2383       +5     
  Misses          411      411              

Flag	Coverage Δ
7.4	85.24% <ø> (+0.02%)	⬆️
8.0	85.28% <ø> (+0.02%)	⬆️
8.1	85.28% <ø> (+0.02%)	⬆️

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Impacted Files	Coverage Δ
src/SDK/Trace/Span.php	93.91% <0.00%> (+0.21%)	⬆️

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