Simplify nestjs-prisma usage with Prisma v7+ database adapter and output path

[marcjulian]

• remove PrismaService with imports to @prisma/client
• rename CustomPrismaService to PrismaService - requires an PrismaClient instance with adapter and output path
• add function for error handle to be reused
• add copy code to docs
• add example for extensions (library/copy)
• add example for error handling

[marcjulian]

Started working on this in #123