Copy/paste settings

# Feature request

Let the user access a text representation of their settings.

## Summary

The desired doc selection and other settings are likely to be the same across machines, browser profiles etc. A way to copy/backup/export and paste/restore/import those settings would make devdocs easier to make your own.

## Examples

Example designs for this feature:

* Put two buttons in settings, one for Copy and one for Paste. Copy will put a serialized representation of all settings into the clipboard and confirm to the user. Paste will read the clipboard, parse/validate the payload and then ask the user whether they're sure they want to overwrite settings.
* Put two buttons in settings, one for downloading a settings file and one for importing settings from a file.
* Put one button in settings that puts a setting restore link into the clipboard. If the user navigates to this URI, they are asked to confirm overwriting the settings.
* Put a textarea in settings that holds a JSON or YAML representation of all settings. All settings can be edited as normal or in the textarea, and the two representations will stay in sync.

No se indica ningún archivo, prueba ni punto de entrada de implementación. Empieza por localizar la pantalla de configuración y cómo se almacenan actualmente las configuraciones; después, aclara qué diseño de exportación/importación y qué configuraciones entran en el alcance. El trabajo terminado debe incluir una interacción acordada, un comportamiento definido de validación y confirmación de sobrescritura, además de pruebas para restauraciones correctas y no válidas.

Escrito por el modelo de indexación a partir del texto del issue.