MongoDB Messenger Transport

This new patch adds support for Symfony 6.

This new patch unlocks the possibility of using the JSON serialization with this transport, because it fixes how headers are handled during serialization.

This new minor adds the resettable option to the transport, so that you can disable it if you need to inspect the transport during tests. This is due to the fact that under Symfony 5.3, if a service implements the ResetInterface (as our transport does), the reset method gets automatically invoked at kernel shutdown, which happens after using the Symfony test client (KernelBrowser).

This other new minor, released on the same day of the previous one, was needed to release support for PHP 8, since it also required to drop support for PHP 7.2 at the same time. Having two separate releases allows end users to have a smoother upgrade path, and me the possibility to release patches in both minors if needed.

This new, first minor of this package handles two issues coming from the upstream, Symfony Messenger package. In both cases the originating cause was the addition of the new ErrorDetailsStamp, which will be the future way to store failure information in messages.