ref https://linear.app/tryghost/issue/DEV-20/faster-builds
- `build` should be the overall script to build the package
- `build:ts` should only build TypeScript
- by having them switched around, `build:ts` would call `yarn build`,
and `yarn` adds several hundreds of milliseconds of time to each build
refs https://github.com/TryGhost/Product/issues/3648
- Refactored Members API RouterController.createCheckoutSession: Split the method into smaller parts so we can reuse individual parts for the upcoming donation checkout session.
- Wired up donation checkout creation
- Added donation events