feat(MQTT): Add enable, disable and enable_on_boot (#4408)

components/mqtt.rst

@@ -34,6 +34,7 @@ Configuration variables:
 ------------------------
 
 - **broker** (**Required**, string): The host of your MQTT broker.
+- **enable_on_boot** (*Optional*, boolean): If enabled, MQTT will be enabled on boot. Defaults to ``true``.
 - **port** (*Optional*, int): The port to connect to. Defaults to 1883.
 - **username** (*Optional*, string): The username to use for
   authentication. Empty (the default) means no authentication.
@@ -733,6 +734,57 @@ Configuration options:
           root["something"] = id(my_sensor).state;
         });
 
+``mqtt.disable`` Action
+-----------------------
+
+This action turns off the MQTT component on demand.
+
+.. code-block:: yaml
+
+    on_...:
+      then:
+        - mqtt.disable:
+
+.. note::
+
+    The configuration option ``enable_on_boot`` can be set to ``false`` if you do not want MQTT to be enabled on boot.
+
+
+``mqtt.enable`` Action
+----------------------
+
+This action turns on the MQTT component on demand.
+
+.. code-block:: yaml
+
+    on_...:
+      then:
+        - mqtt.enable:
+
+.. note::
+
+    The configuration option ``enable_on_boot`` can be set to ``false`` if you do not want MQTT to be enabled on boot.
+    ``mqtt.enable`` can be useful for custom setups. For example, if the broker name is negotiated dynamically and saved in a global variable.
+
+.. code-block:: yaml
+
+    mqtt:
+      id: mqtt_id
+      broker: ""
+      enable_on_boot: False
+
+    globals:
+      - id: broker_address
+        type: std::string
+        restore_value: yes
+        max_restore_data_length: 24
+        initial_value: '"192.168.1.2"'
+
+    on_...:
+      then:
+        - lambda: !lambda id(mqtt_id).set_broker_address(id(broker_address));
+        - mqtt.enable:
+
 .. _mqtt-connected_condition:
 
 ``mqtt.connected`` Condition