Add an in-room reminder to set up key recovery

This adds an in-room reminder above the message timeline to set up Secure
Message Recovery so that your keys will be backed up. If you try to ignore it,
an additional dialog is shown to confirm.

Fixes vector-im/riot-web#7783.

Signed-off-by: J. Ryan Stinnett <jryans@gmail.com>

src/settings/Settings.js

@@ -151,6 +151,11 @@ export const SETTINGS = {
         displayName: _td('Always show encryption icons'),
         default: true,
     },
+    "showRoomRecoveryReminder": {
+        supportedLevels: LEVELS_ACCOUNT_SETTINGS,
+        displayName: _td('Show a reminder to enable Secure Message Recovery in encrypted rooms'),
+        default: true,
+    },
     "enableSyntaxHighlightLanguageDetection": {
         supportedLevels: LEVELS_ACCOUNT_SETTINGS,
         displayName: _td('Enable automatic language detection for syntax highlighting'),