Deploy commands

[Wulfheart]

Hello,

I would like to have the option to define a script that is executed on each deployment as I want to backup my database before each deployment.
I thought about doing it in the docker container but this doesn't work as the docker container shouldn't be concerned with DB backups. But as we don't know in which environment it will be run I guess it would be helpful to specify a docker container which will be executed as part of the deployment process. I think it cannot be part of the build process as there can also be external build with e.g. GitHub Actions.

@andrasbacsai If you would be willing to merge such a feature I could write a concept for it and eventually implement it if you don't have the time or bandwidth for it right now.