We currently parse payloads through json_decode as:

• \stdClass for most of them
• PhabricatorStory for Phabricator ones

Plan is instead to:

• create an abstract BasePayload class (probably empty?)
• create classes for GitHub (see T595), DockerHub, Jenkins, etc. payloads
• PhabricatorStory should inherit too
• map objects deserialized with json_decode to these new classes

This will have several benefits:

• we know everywhere an object is payload
• we can add an explicit return type at Nasqueron\Notifications\Console\Commands\NotificationsPayload::formatPayload() (currently an @return PhabricatorStory|stdClass)

good-first-issue — This task has been especially identified as suitable to discover our code base.

We use JSON mapper to map JSON payloads to classes.