Add semantic segmentation example script, no trainer
# What does this PR do?

This PR adds an example script regarding fine-tuning any model supported by the `AutoModelForSemanticSegmentation` API on a semantic segmentation dataset, including regularly pushing to the hub during training as well as WandB logging.

I switched to using Accelerate as I had a bug with the Trainer. 

To do:

- [ ] fix Tensorboard logs
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_16630). All of your documentation changes will be reflected on that endpoint.<|||||>I've added all requested changes. As you can see, I'm updating the repo using commits rather than creating subfolders.<|||||>Updated the script to create subfolders like the other examples (and these aren't pushed to the hub based on the gitignore file).<|||||>Some issue with git, closing this PR in favor of a new one.