Canned Messages via InkHUD menu (#7096)

* Allow observers to respond to AdminMessage requests
Ground work for CannedMessage getters and setters

* Enable CannedMessage config in apps for InkHUD devices

* Migrate the InkHUD::Events AdminModule observer
Use the new AdminModule_ObserverData struct

* Bare-bones NicheGraphics util to access canned messages
Handles loading and parsing. Handle admin messages for setting and getting.

* Send canned messages via on-screen menu

* Change ThreadedMessageApplet from Observer to Module API
Allows us to intercept locally generated packets ('loopbackOK = true'), to handle outgoing canned messages.

* Fix: crash getting empty canned message string via Client API

* Move file into Utils subdir

* Move an include statement from .cpp to .h

* Limit strncpy size of dest, not source
Wasn't critical in ths specific case, but definitely a mistake.

src/modules/AdminModule.h

@@ -6,10 +6,19 @@
 #include "mesh/wifi/WiFiAPClient.h"
 #endif
 
+/**
+ * Datatype passed to Observers by AdminModule, to allow external handling of admin messages
+ */
+struct AdminModule_ObserverData {
+    const meshtastic_AdminMessage *request;
+    meshtastic_AdminMessage *response;
+    AdminMessageHandleResult *result;
+};
+
 /**
  * Admin module for admin messages
  */
-class AdminModule : public ProtobufModule<meshtastic_AdminMessage>, public Observable<const meshtastic_AdminMessage *>
+class AdminModule : public ProtobufModule<meshtastic_AdminMessage>, public Observable<AdminModule_ObserverData *>
 {
   public:
     /** Constructor