Update notification popups are annoying when vscode/vscodium is
managed by Home Manager. However, as these settings also require the
configuration to be managed via `userSettings`, they are disabled by
default.
Adds a new `keybindings` option to the `vscode` configuration.
It contains a list of key bindings, which will be written to
`%vscode-dir%/User/keybindings.json`.
PR #1351
