chore: filled in project structure

Added some example basic files containing a functioning /message
endpoint which logs the received message to INFO.

ref: N25B-144

src/control_backend/api/v1/router.py

@@ -0,0 +1,15 @@
+from fastapi.routing import APIRouter
+
+from control_backend.api.v1.endpoints import message, sse
+
+api_router = APIRouter()
+
+api_router.include_router(
+    message.router,
+    tags=["Messages"]
+)
+
+api_router.include_router(
+    sse.router,
+    tags=["SSE"]
+)