Support a config option to change the default device name (#20790)

docs/config.md

@@ -166,6 +166,8 @@ For a good example, see https://develop.element.io/config.json.
   the well-known location is used instead.
 1. `analyticsOwner`: The entity that analytics data is being sent to. Used in copy
    when explaining to the user where data is being sent. If not set, defaults to `brand`.
+1. `defaultDeviceDisplayName`: The default device display name to use for new logins
+   and registrations. If not set then a calculated version will be used.
 
 Note that `index.html` also has an og:image meta tag that is set to an image
 hosted on riot.im. This is the image used if links to your copy of Element

src/vector/app.tsx

@@ -180,6 +180,8 @@ export async function loadApp(fragParams: {}) {
         return;
     }
 
+    const defaultDeviceName = config['defaultDeviceDisplayName'] ?? platform.getDefaultDeviceDisplayName();
+
     const MatrixChat = sdk.getComponent('structures.MatrixChat');
     return <MatrixChat
         onNewScreen={onNewScreen}
@@ -190,7 +192,7 @@ export async function loadApp(fragParams: {}) {
         enableGuest={!config.disable_guests}
         onTokenLoginCompleted={onTokenLoginCompleted}
         initialScreenAfterLogin={getScreenFromLocation(window.location)}
-        defaultDeviceDisplayName={platform.getDefaultDeviceDisplayName()}
+        defaultDeviceDisplayName={defaultDeviceName}
     />;
 }