MongoDB Messenger Transport

This new minor should just add support for Symfony 7, but in reality it contains a lot of work. The CI for this library wasn’t active for a long time, so a lot of issues and deprecations where making it fail…

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.