[Conditional, Deformable DETR] Add postprocessing methods
# What does this PR do?

This PR adds `post_process_object_detection` to Conditional DETR and Deformable DETR's feature extractors. They both use the same postprocessing (and it's different from original DETR + YOLOS).

It also removes methods which aren't necessary: YOLOS and Deformable DETR don't have a segmentation head model, so no `post_process_segmentation` methods are needed for those models.

To do:

- [x] add corresponding tests
- [x] remove legacy segmentation postprocessing methods of conditional DETR, add new ones
_The documentation is not available anymore as the PR was closed or merged._<|||||>> Could you add Conditional DETR to MODEL_FOR_XXX_SEGMENTATION_MAPPING_NAMES?

Do you mean I need to add the model to all 3 segmentation mapping names? Cause that isn't the case with DETR either

<|||||>> > Could you add Conditional DETR to MODEL_FOR_XXX_SEGMENTATION_MAPPING_NAMES?
> 
> Do you mean I need to add the model to all 3 segmentation mapping names? Cause that isn't the case with DETR either

`MODEL_FOR_IMAGE_SEGMENTATION_MAPPING_NAMES` is marked for deprecation and there is no `MODEL_FOR_PANOPTIC_SEGMENTATION_MAPPING_NAMES`,  I meant we can create one and add DETR and MaskFormer to panoptic mapping, along with Conditional DETR.
<|||||>Ok, let's do that in a separate PR.