Add Generic Command Registration (#11)

**Rationale:**

Realized that #10 did not include any way to register commands without going through the IntoCommandDefinition trait.

**Changes:**

- Adds a method to register a raw command handler

Reviewed-on: #11
Co-authored-by: Sergey Savelyev <sergeysav.nn@gmail.com>
Co-committed-by: Sergey Savelyev <sergeysav.nn@gmail.com>

api/src/client/telemetry.rs

@@ -362,10 +362,7 @@ mod tests {
             .unwrap()
             .unwrap();
         // This should block as there should not be space in the queue
-        assert!(tlm_handle
-            .publish_now(false)
-            .now_or_never()
-            .is_none());
+        assert!(tlm_handle.publish_now(false).now_or_never().is_none());
 
         let tlm_msg = timeout(Duration::from_secs(1), rx.recv())
             .await