Add contract declaration

[minenwerfer]

Contracts are DTOs plus access control directives: https://github.com/aeria-org/aeria/blob/9c98734bc5d89831d9fce8980abc4a9fa870601f/packages/types/src/contract.ts#L20

Simplest form:

contract Test {
  roles {
    root
    customer
  }
  query {
    properties {
      name str
    }
  }
}

Outputs:

export const test = defineContract({
  roles: [
    'root',
    'customer',
  ],
  query: {
    type: 'object',
    properties: {
      name: {
        type: 'string',
      },
    },
  },
})

---

With unions:

contract Test {
  roles {
    root
    customer
  }
  // inspired by TypeScript union syntax
  query
    | {
      properties {
        type const @value("by_name")
        name str
      }
    }
    | {
      properties {
        val const @value("by_age")
        age int
      }
    }
}

Outputs:

export const test = defineContract({
  roles: [
    'root',
    'customer',
  ],
  query: [
    {
      type: 'object',
      properties: {
        type: { const: 'by_name', },
        name: { type: 'string', },
      },
    },
    {
      type: 'object',
      properties: {
        type: { const: 'by_age', },
        age: { type: 'integer', },
      },
    },
  ],
})