Add changelog for 2.1.2
Add changelog for 2.1.2

Cherry pick of https://github.com/jupyterlab/jupyterlab/commit/bc95c579c9ea24b9b159571887a6e09590a6e8b0

jupyter/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab