Add `OwlViTForObjectDetection` to `MODEL_FOR_OBJECT_DETECTION`
# What does this PR do?

~~This seems a miss, but need @NielsRogge to make sure.~~

well, he told me

> it's not a bug, it's intended. OWL-ViT can be loaded using the AutoModelForZeroShotObjectDetectionModel class (few that's a long name)
well<|||||>The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_24992). All of your documentation changes will be reflected on that endpoint.