Add a new page to the MLIR documentation that links to the upstream Lighthouse project as well as additional third-party tutorials. The goal is to make it easier for newcomers to discover MLIR learning resources beyond the Toy tutorial. The underlying discussion/RFC can be found [here](https://discourse.llvm.org/t/rfc-tutorial-a-beginner-friendly-end-to-end-mlir-compiler-pipeline/89788).