[MM-22013] - Allow users to specify default download locations (#1383)

* [MM-22013] - Allow users to specify default download locations

* PR comments

* Add proper config prop

* Update src/browser/components/SettingsPage.jsx

Co-authored-by: Guillermo Vayá <guillermo.vaya@mattermost.com>

* Remove string ref

* Fix styling

* Update styling

* Disable input

* Add variable for windows

* Prevent dialog from opening twice

Co-authored-by: Nevyana Angelova <nevyangelova@Nevyanas-MBP-2.fritz.box>
Co-authored-by: Nevyana Angelova <nevyangelova@Nevyanas-MacBook-Pro-2.local>
Co-authored-by: Guillermo Vayá <guillermo.vaya@mattermost.com>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

src/common/config/defaultPreferences.js

@@ -23,6 +23,7 @@ const defaultPreferences = {
   autostart: true,
   spellCheckerLocale: 'en-US',
   darkMode: false,
+  downloadLocation: `/Users/${process.env.USER || process.env.USERNAME}/Downloads`
 };
 
 export default defaultPreferences;