add 4.3 documentation

docs/users/jupyterlab/4.2/index.md

docs/users/jupyterlab/4.3/index.md

docs/users/jupyterlab/4.3/kernels_cloud_venv.ipynb

docs/users/jupyterlab/4.3/kernels_hpc_conda.ipynb

docs/users/jupyterlab/4.3/kernels_hpc_modify_runtime.ipynb

docs/users/jupyterlab/4.3/kernels_hpc_pyenv.ipynb

docs/users/jupyterlab/4.3/kernels_hpc_singularity.ipynb

docs/users/jupyterlab/4.3/kernels_hpc_venv.ipynb

mkdocs.yml