[MM-36456] Add support for Gnome's do-not-disturb (#2278)

* Add support for gnome do-not-disturb mode

* Add tests

* Invert condition

src/main/notifications/dnd-linux.ts

@@ -0,0 +1,23 @@
+// Copyright (c) 2016-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+import {execSync} from 'child_process';
+
+import log from 'electron-log';
+
+const GNOME_READ_DND = 'gsettings get org.gnome.desktop.notifications show-banners';
+
+function getLinuxDoNotDisturb() {
+    try {
+        const showNotifications = execSync(GNOME_READ_DND).toString().replace('\n', '');
+        log.debug('getLinuxDoNotDisturb', {showNotifications});
+
+        return showNotifications !== 'true';
+    } catch (error) {
+        log.error('getLinuxDoNotDisturb Error:', {error});
+
+        return false;
+    }
+}
+
+export default getLinuxDoNotDisturb;