add customizable ending learning rate arguments to warmup schedulers
# What does this PR do?

I noticed that in the original implementation, the learning rate for cosine and linear scheduler with warmup is always scheduled to 0. However, in many new research such as Masked Autoencoder, BEiT, they scheduled the learning rate to some no 0 end learning rate (1e-6 in their case). Hence, I added this features for these schedulers, so people who don't want to schedule learning rate directly to 0 can also use huggingface schedulers.

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [X] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [ ] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [X] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?

## Who can review?

@Narsil 
@sgugger

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_21434). All of your documentation changes will be reflected on that endpoint.<|||||>Not sure I can properly review this code, sorry I never touch that file.<|||||>Thank you for your PR, but the Transformers library is primarily a library of models. Those schedulers are just implemented for ease of use in our Trainer (which wouldn't be able to set that `end_lr` new argument), anything more involved should come from another library/custom user code :-)<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.