text: Title: Add support for overwriting datasources
  Body: ## Problem
  
  <!-- A clear and concise description of what the problem is. Ex. I'm always frustrated when [...] -->
  
  Prisma supports dynamically overriding datasources:
  
  ```ts
  import { PrismaClient } from '@prisma/client'
  
  const prisma = new PrismaClient({
    datasources: {
      db: {
        url: 'file:./dev_qa.db',
      },
    },
  })
  ```
  
  ## Suggested solution
  
  <!-- A clear and concise description of what you want to happen. -->
  
  We could make a slight improvement to this API by making it singular and removing the requirement to name the datasource. Prisma chose the above API for forwards compatibility, I am okay with having to make changes to this in the future.
  
  ```py
  from prisma import Client
  
  client = Client(
      datasource={
          'url': 'file:./dev_qa.db',
      },
  )
  ```
  