Add CORS headers to API responses

src/api_main.py

@@ -169,6 +169,11 @@ async def get_stats(request: web.Request, conn):
         "messages": message_count
     })
 
+@web.middleware
+async def add_cors_headers(request, handler):
+    resp = await handler(request)
+    resp.headers["Access-Control-Allow-Origin"] = "*";
+    return resp
 
 @web.middleware
 async def render_pk_errors(request, handler):
@@ -178,7 +183,7 @@ async def render_pk_errors(request, handler):
         raise web.HTTPBadRequest(body=e.message)
 
 
-app = web.Application(middlewares=[render_pk_errors])
+app = web.Application(middlewares=[render_pk_errors, add_cors_headers])
 app.add_routes([
     web.get("/systems/{id}", get_system),
     web.get("/systems/{id}/switches", get_switches),