Feature request: Mimetype set in LanguageInfo

I am currently trying to create a VTL Language Server, and running into a similar issue as [here](https://github.com/jupyter-lsp/jupyterlab-lsp/issues/384#issuecomment-767139017)

For it's integration with Jupyter Lab and possibly other IDEs, I believe the server called is based on the [mimetype returned by the active kernel](https://jupyter-client.readthedocs.io/en/stable/messaging.html#kernel-info:~:text=in%20this%20language-,%27mimetype%27%3A%20str%2C,-%23%20Extension%20including%20the)

I would like to further populate the [LanguageInfo](https://github.com/InseeFrLab/Trevas-Jupyter/blob/f08cd4ae99a0cbd4885d9a577a65d41ceaf2b854/src/main/java/fr/insee/trevas/jupyter/VtlKernel.java#L39C25-L39C37) to additionally include `mimetype` as `text/vtl` instead of the current default of `text/plain`