Changes

Uses own TS config for DatoCMS migrations (config/datocms/tsconfig.json) so it doesn't conflict with the TS config for the rest of the project (/tsconfig.json).
Removes "type": "module" from package.json so DatoCMS migrations correctly parse migration TS files.
[ ] Resolves specific errors thrown when running npm migrations:run ....
[ ] Removes warning on running migrations from docs/getting-started.md.

Associated issue

Resolves #62 .

[ ] I have performed a self-review of my own code
[ ] I have made sure that my PR is easy to review (not too big, includes comments)
[ ] I have added/updated tests to prove that my feature works (if not possible please explain why)
[ ] I have made changes to the README and if the change affects the project setup (npm commands changed, new service added, environmental variable added)
[ ] I have added a decision log entry if the change affects the architecture or changes a significant technology
[ ] I have notified a reviewer