Defining jupytext as the default viewer for text notebooks under jlab4

JupyterLab extensions
2

here is where i set default viewers in jlab4:

~/ cat .jupyter/lab/user-settings/@jupyterlab/docmanager-extension/plugin.jupyterlab-settings
{
    "autosave": true,
    "autosaveInterval": 120,
    "confirmClosingDocument": false,
    "lastModifiedCheckMargin": 500,
    "renameUntitledFileOnSave": true,
    "defaultViewers": {
        "markdown": "Editor",
        "json": "Editor",
        "csv": "Editor",
        "tsv": "Editor"
    }
}

edit: also available under settings → document manager