[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/main/Validator.js

@@ -80,6 +80,7 @@ const configDataSchemaV2 = Joi.object({
   autostart: Joi.boolean().default(true),
   spellCheckerLocale: Joi.string().regex(/^[a-z]{2}-[A-Z]{2}$/).default('en-US'),
   darkMode: Joi.boolean().default(false),
+  downloadLocation: Joi.string(),
 });
 
 // eg. data['community.mattermost.com'] = { data: 'certificate data', issuerName: 'COMODO RSA Domain Validation Secure Server CA'};