Begin of the insertionChanges in API behavior:End of the insertion Begin of the deletion TODO:End of the deletion

* Begin of the insertionIntroduce a new endpoint `POST /api/v3/file_links`.
* The request/response signature is similar to `POST /api/v3/work_packages/{id}/file_links`, but there is no work\_package known during the request time. Therefore, we create a file\_link without a containerEnd of the insertion Begin of the deletion add necessary migrations (container idEnd of the deletion and Begin of the insertionrespond without aEnd of the insertion container Begin of the insertionlink.
* Implementation notes:
* toEnd of the insertion Begin of the deletion type canEnd of the deletion be Begin of the insertionable to create file\_links without a known container we have to remove not null constraints from the `file_links.container_id` and `file_links.container_type`  database columns.
End of the insertion Begin of the deletion `null`)
End of the deletion * Begin of the insertionwe haveEnd of the insertion Begin of the deletion add cleanup of uncontainered file linksEnd of the deletion to Begin of the insertioncover a case when file\_links has been created, but work\_package create form has never been confirmed. To do it we can introduce aEnd of the insertion cron job Begin of the insertionfor cleaning up.
`app/workers/attachments/cleanup_uncontainered_job.rb` - theEnd of the insertion Begin of the deletion (sameEnd of the deletion one Begin of the deletion likeEnd of the deletion for Begin of the insertionhandle a similar case for attachments. 
* Modify `POST` [`https://openproject.local/api/v3/work_packages`](https://openproject.local/api/v3/work_packages)
* It should accept a list of file\_links by analogy to attachments. And respond with them afterwards. 
* Implementation note: the file\_links have to be bound to a container (work\_package in this case). The logic for attachments bindings is located in `app/services/attachments/set_replacements.rb`End of the insertion Begin of the deletion attachments?)End of the deletion