feat: Add stores for copilotMessages and copilotThreads (#11603)

- Set up stores for copilotThreads and copilotMessages.
- Add support for upsert messages to the copilotMessages store on
receiving ActionCable events.
- Implement support for the upsert option.

app/javascript/dashboard/store/captain/copilotMessages.js

@@ -0,0 +1,19 @@
+import CopilotMessagesAPI from 'dashboard/api/captain/copilotMessages';
+import { createStore } from './storeFactory';
+
+export default createStore({
+  name: 'CopilotMessages',
+  API: CopilotMessagesAPI,
+  getters: {
+    getMessagesByThreadId: state => copilotThreadId => {
+      return state.records.filter(
+        record => record.copilot_thread?.id === Number(copilotThreadId)
+      );
+    },
+  },
+  actions: mutationTypes => ({
+    upsert({ commit }, data) {
+      commit(mutationTypes.UPSERT, data);
+    },
+  }),
+});