Add initial Matrix end-to-bridge encryption support

mautrix_telegram/example-config.yaml

@@ -191,6 +191,17 @@ bridge:
             height: 256
             background: "020202"  # only for gif
             fps: 30               # only for webm
+    # End-to-bridge encryption support options. These require matrix-nio to be installed with pip
+    # and login_shared_secret to be configured in order to get a device for the bridge bot.
+    #
+    # Additionally, https://github.com/matrix-org/synapse/pull/5758 is required if using a normal
+    # application service.
+    encryption:
+        # Allow encryption, work in group chat rooms with e2ee enabled
+        allow: false
+        # Default to encryption, force-enable encryption in all portals the bridge creates
+        # This will cause the bridge bot to be in private chats for the encryption to work properly.
+        default: false
 
     # Overrides for base power levels.
     initial_power_level_overrides: