How to extent Spring Petclinic so that a single installation (instance) can be used for diferent veterinarians

Imagine that your Spring Petclinic software (Petclinic is only an example but can be any software) is running perfectly and you would now like to sell your software to several companies. How would you change the Petclinic so that each Petclinic run in own instance but in a singele enviroment?

Of course, the simplest solution would be to install and run each Petclinic in a different enviroment, but How to changed the program so that one single installation can be use for all companies.

Which architecture pattern or which procedure should be used here?

something like:

abstract class AbstratPetclinic {
   createPetclinic();
}

class SafariPetclinicFabric extends AbstratPetclinic() {

    createPetclinic() {
      ...
    }
}

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