Summary:
## Motivation

The recent website upgrade moved the location of tutorials and api reference breaking existing links to those. Here we fix those links and also configure Docusaurus to raise an error on broken links in the future.

Pull Request resolved: https://github.com/pytorch/botorch/pull/2720

Test Plan:
Docusaurus checks for broken links when creating a production build. Running `./scripts/build_docs.sh -b` now results in a clean build with no broken links reported.

## Related PRs
- https://github.com/pytorch/botorch/pull/2715

Reviewed By: saitcakmak, Balandat

Differential Revision: D69034874

Pulled By: CristianLara

fbshipit-source-id: 3a3c9488a6bb1c0a21d0cbb854972e84432eb467