feat: enable subscription logic for messengers

In order to help control traffic over the websocket, a subscription feature has been added:
* A config option, `enableMessengerSubscriptions` has been added
* When true, the MessengerBase class will assume that any message sent using the `PostStatusMessage` that has a valid client ID wants to send any subsequent unsolicited updates to that same client
* The client's ID will be added a list of subscribed client IDs
* Any subsequent messages sent using the `PostStatusMessage` methods that have a null clientId will ONLY be sent to subscribed clients
* When a client disconnects, it will be removed from the list of subscribed clients

This should cut down drastically on the traffic to the UI, especially when combined with requesting partial status updates from a device rather than the entire state.

src/PepperDash.Essentials.MobileControl/MobileControlConfig.cs

@@ -38,6 +38,12 @@ namespace PepperDash.Essentials
         /// </summary>
         [JsonProperty("enableApiServer")]
         public bool EnableApiServer { get; set; } = true;
+
+        /// <summary>
+        /// Enable subscriptions for Messengers
+        /// </summary>
+        [JsonProperty("enableMessengerSubscriptions")]
+        public bool EnableMessengerSubscriptions { get; set; }
     }
 
     /// <summary>
@@ -78,6 +84,15 @@ namespace PepperDash.Essentials
         [JsonProperty("csLanUiDeviceKeys")]
         public List<string> CSLanUiDeviceKeys { get; set; }
 
+        /// <summary>
+        /// Get or set the Secure property
+        /// </summary>
+        /// <remarks>
+        /// Indicates whether the connection is secure (HTTPS).
+        /// </remarks>
+        [JsonProperty("Secure")]
+        public bool Secure { get; set; }
+
         /// <summary>
         /// Initializes a new instance of the MobileControlDirectServerPropertiesConfig class.
         /// </summary>