Describe the bug
day.add does not have valid type safety because of the ManipulateType type

Expected behavior
Passing an invalid unit to dayjs.add will result in a type error.

Information

• Day.js Version [1.11.1]
• OS: [macOS 12.3.1]
• Browser [N/A]
• Time zone: [CDT]

Repro:

dayjs().add(4, 'millenniums') // Should result in: Type '"millenniums"' is not assignable to type 'ManipulateType'
// const nope: OpUnitType = 'millenniums'; // ❌ Type '"millenniums"' is not assignable to type 'OpUnitType'