reorganizes the code, introduces preference slice

frontend/src/preferences/preferenceSlice.ts

@@ -0,0 +1,29 @@
+import { createSlice } from '@reduxjs/toolkit';
+import store from '../store';
+
+interface Preference {
+  apiKey: string;
+}
+
+const initialState: Preference = {
+  apiKey: '',
+};
+
+export const prefSlice = createSlice({
+  name: 'preference',
+  initialState,
+  reducers: {
+    setApiKey: (state, action) => {
+      state.apiKey = action.payload;
+    },
+  },
+});
+
+export const { setApiKey } = prefSlice.actions;
+export default prefSlice.reducer;
+
+type RootState = ReturnType<typeof store.getState>;
+
+export const selectApiKey = (state: RootState) => state.preference.apiKey;
+export const selectApiKeyStatus = (state: RootState) =>
+  !!state.preference.apiKey;