This PR specifically introduces a `core` folder and moves the following packages over, without any other changes:
- `api/backend`
- `api/config`
- `api/options`
- `api/schema`
Once this is merged and we confirm there's no regressions, I can migrate over the remaining changes piece by piece to split up application startup, backend services, http, and mqtt as was the goal of the earlier PRs!
* Initial implementation of upload files api.
* Move sanitize method to utils.
* Save uploaded data to uploads folder.
* Avoid loop if we do not have a purpose.
* Minor cleanup of api and fix bug where deleting duplicate filename cause error.
* Revert defer of saving config
* Moved creation of directory to startup.
* Make file names unique when storing on disk.
* Add test for files api.
* Update dependencies.
