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/graphics/niche/InkHUD/Applets/System/Menu/MenuPage.h

@@ -18,6 +18,7 @@ namespace NicheGraphics::InkHUD
 enum MenuPage : uint8_t {
     ROOT, // Initial menu page
     SEND,
+    CANNEDMESSAGE_RECIPIENT, // Select destination for a canned message
     OPTIONS,
     APPLETS,
     AUTOSHOW,