Allow the generator execution to be disabled

[aiji42]

I have a need to intentionally stop zod-prisma generation, for example when running prisma generate on CI.

It would be useful to be able to temporarily disable it via an environment variable. e.g. ZOD_PRISMA_DISABLE=true yarn prisma generate.

[chrishoermann]

I'm late to the show but I just published a similar generator (zod-prisma-types) that lets you define in which environment it should be run.