feat(appservice-discord): add disablePortalBridging bridge option

This allows disabling the automatic portal bridging, meaning bridges
must be manually setup via self-servicing, by setting:

    matrix_appservice_discord_bridge_enableSelfServiceBridging: true

roles/matrix-bridge-appservice-discord/defaults/main.yml

@@ -42,6 +42,7 @@ matrix_appservice_discord_bridge_domain: "{{ matrix_domain }}"
 matrix_appservice_discord_bridge_homeserverUrl: "{{ matrix_homeserver_url }}"
 matrix_appservice_discord_bridge_disablePresence: false
 matrix_appservice_discord_bridge_enableSelfServiceBridging: false
+matrix_appservice_discord_bridge_disablePortalBridging: false
 
 # Database-related configuration fields.
 #

roles/matrix-bridge-appservice-discord/templates/config.yaml.j2

@@ -28,6 +28,8 @@ bridge:
   disableJoinLeaveNotifications: false
   # Disable Invite echos from matrix
   disableInviteNotifications: false
+  # Disable portal briding (automatic room creation)
+  disablePortalBridging: {{ matrix_appservice_discord_bridge_disablePortalBridging|to_json }}
   # Auto-determine the language of code blocks (this can be CPU-intensive)
   determineCodeLanguage: false
 # Authentication configuration for the discord bot.