transformers Add post_process_depth_estimation to image processors

Feature request

The image processors of depth estimation models could benefit from a post_process_depth_estimation method, similar to the post_process_object_detection, post_process_semantic_segmentation methods.

This includes:

[ ] DPT
[ ] Depth Anything (and v2)
[ ] ZoeDepth (soon: #30136) => this one requires some special postprocessing logic as shown in this notebook

Motivation

People now need to manually interpolate the predicted depth to the original size of the image as seen here.

The interpolation could be replaced by a simple image_processor.post_process_depth_estimation method which postprocesses the predicted depth and interpolates it to the original image size.