Adds config.db.prismaSchemaPath

[dcousens]

Following in the theme of #8773 by @marekryb , this pull request adds config.db.prismaSchemaPath.

As in the changes I made to #8773, I have opted to use the examples/ and their strict postinstall adherence as the method to test this functionality, which our CI is testing against.

Unfortunate that we need to prefix config.db.* options with prisma*, as we did not refer to config.db as config.prisma, but maybe we can change that one day and be consistent between our config.types, config.graphql and config.prisma configurations.

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