feat: collections can use custom database operations

[kendelljoseph]

Description

Adds option to override default database operations for a collection

import { CollectionConfig } from 'payload/types';

const Collection: CollectionConfig = {
  slug: 'example-collection',
  // Database operations for this collection  
  db: {
    create: () => {},
    deleteMany: () => {},
    deleteOne: () => {},
    find: () => {},
    findOne: () => {},
    updateOne: () => {}
  },
  fields: [
    {
      name: 'someField',
      type: 'text',
    },
  ],
}

export default Collection;

Type of change

• [x] New feature (non-breaking change which adds functionality)
• [ ] This change requires a documentation update

Checklist:

• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] Existing test suite passes locally with my changes
• [ ] I have made corresponding changes to the documentation