Register Doctrine Tracing Instrumentation on available connections

[gaelreyrol]

We should register Doctrine Tracing Middleware on available Doctrine connections using parameters doctrine.connections.

It should be done after Doctrine compiler pass: https://github.com/doctrine/DoctrineBundle/blob/75026f2e42f7ab93a4d4cfb766cb69b50dd99240/src/DoctrineBundle.php#L57.