Custom creation date

[denniswittich]

Add possibility to set a custom creation date when running detections or uploading images.

This PR slightly exploded because I stumbled across the following issue:
the nodelib used a dataclass "Detections" which was used by the trainer when uploading detections and by the detector when uploading pairs of images and detections.

However, this is not correct because two different EPs are accessed. While both of them require detections, the image_upload also deals with image metadata such as the creation date of THE IMAGE, tags and the source field.
The other one takes detections and a single other field image_id to assign the detections to the correct image.

Before, a mixture of those two structures was used which I found completely confusing, lazy and wrong.

So I fixed this which leads to a breaking change of the library because detectors should from now on use the data structure "ImageMetadata"