Update span name if route is known

[cedricziel]

As per the semantic conventions, span names should include the route name if available:

HTTP server span names SHOULD be {method} {http.route} if there is a (low-cardinality) http.route available (see below for the exact definition of the {method} placeholder).

This changes updates the span names for the Symfony auto-instrumentation to use {http.request.method} {http.route} in cases where it is available.

[codecov]

Codecov Report

Merging #205 (d65a549) into main (a66b1f1) will increase coverage by 0.51%.
The diff coverage is 0.00%.

❗ Current head d65a549 differs from pull request most recent head 230ae91. Consider uploading reports for the commit 230ae91 to get more accurate results

@@             Coverage Diff              @@
##               main     #205      +/-   ##
============================================
+ Coverage     33.13%   33.65%   +0.51%     
+ Complexity      852      839      -13     
============================================
  Files            76       75       -1     
  Lines          3247     3197      -50     
============================================
  Hits           1076     1076              
+ Misses         2171     2121      -50     

Flag	Coverage Δ
7.4	46.34% <ø> (ø)
8.0	32.70% <0.00%> (-0.36%)	⬇️
8.1	35.93% <0.00%> (+2.83%)	⬆️
8.2	36.91% <0.00%> (+3.83%)	⬆️

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Files	Coverage Δ
...rumentation/Symfony/src/SymfonyInstrumentation.php	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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