Move all Prisma-related operations and packages to the project's top level

[sodic]

In Wasp's new structure (prototyped in #1584), @prisma/client is either an SDK dependency or a project dependency, possibly both (see #1595 for details).
It therefore makes most sense to make the prisma package a project dependency.

Anticipated tasks:

• Modify the generator to list prisma as a dependency in the project's package.json file.
• Decide where to list the @prisma/client dependency.
• Verify all Prisma operations successfully execute at the project's top level.
• Verify everything's OK with the types and the IDE support.

[sodic]

Closed with #1604

We've had to make some compromises (e.g., where Prisma is executed).