[2.x] Adds health check command

[joedixon]

This PR adds a new hidden command to the Vapor Core which will be used during deployment to determine whether or not an environment being deployed is healthy or not.

Updates to the tests are due to an change to laminas-diactoros

[williamjulianvicary]

This broke my builds on v2.28 of Vapor Core somehow. Upgrading to the latest release sorted the issue:

Unable to obtain a healthy response from the environment being deployed. Please check the logs for more information.

Sentry reported: Command "vapor:health-check" is not defined.

[joedixon]

Thanks for reporting. Vapor will only run vapor:health-check if it detects a compatible version of Vapor Core in the composer.json file, so it seems as though there was a version mismatch somewhere.