* fixing w3c-tracecontext test startup
make w3c-trace-context was suffering from some bitrot, so this change gets it building and
running again. The tests themselves still fail due to further code-related bitrot.
* silence new phpstan error
* Add W3C trace context test service
* Add README
* style formatting
* Update test service to use local files
* fix phpstan suppression
* ignore phpstan and psalm errors
* lock symfony version to 5.2
* cleanup
* more cleanup