add deprecation notices to MQTT service docs

Mark the MQTT section in the Services docs and the MQTT_Type reference
page as deprecated, directing users to the new MQTT connector or HTTP
API.

Author: FabianoEger

docs/source/Services/MQTT_Type.rst

@@ -1,6 +1,11 @@
 **MQTT Type**
 ===============
 
+.. deprecated::
+    Legacy MQTT is deprecated and will be removed in a future major version.
+    Migrate to the new MQTT connector or use the HTTP API.
+    See: https://docs.tago.io/docs/tagoio/integrations/networks/mqtt/
+
 .. _mqtt_options:
 
 options

docs/source/Services/index.rst

@@ -100,6 +100,11 @@ Send Email
 MQTT
 ====
 
+.. deprecated::
+    Legacy MQTT is deprecated and will be removed in a future major version.
+    Migrate to the new MQTT connector or use the HTTP API.
+    See: https://docs.tago.io/docs/tagoio/integrations/networks/mqtt/
+
 Publish to a MQTT Device
 
     **Parameters:**