Updated the mutation to reactively update messages

...ssets/javascripts/ai/components/ai_genie_chat_message.vue

ee/app/assets/javascripts/ai/graphql/chat.mutation.graphql

ee/app/assets/javascripts/ai/tanuki_bot/components/app.vue

ee/app/assets/javascripts/ai/tanuki_bot/store/actions.js

ee/app/assets/javascripts/ai/tanuki_bot/store/mutations.js

...subscriptions/ai_completion_response.subscription.graphql

ee/spec/frontend/ai/components/ai_genie_chat_message_spec.js

.../frontend/ai/components/generate_test_file_drawer_spec.js

ee/spec/frontend/ai/tanuki_bot/components/app_spec.js

ee/spec/frontend/ai/tanuki_bot/mock_data.js

ee/spec/frontend/ai/tanuki_bot/store/actions_spec.js

ee/spec/frontend/ai/tanuki_bot/store/mutations_spec.js

...end/batch_comments/components/summarize_my_review_spec.js

...merge_request_widget/components/ai_commit_message_spec.js

...xplain_vulnerability/explain_vulnerability_drawer_spec.js