[TASK] New SignalSlot after preInit in EditDocumentController

Adds a new SignalSlot possibility after the preInit method call.

Resolves: #56195
Releases: 6.2
Change-Id: Ia68734999a0e5fbe6c945d9e28d8571cd6192e75
Reviewed-on: https://review.typo3.org/27777
Reviewed-by: Tomas Norre Mikkelsen
Tested-by: Tomas Norre Mikkelsen
Reviewed-by: Erik Frister
Tested-by: Erik Frister
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring