Add a network action to fetch the MR Metadata from the API endpoint

app/assets/javascripts/mr_notes/stores/actions.js

+import axios from '~/lib/utils/axios_utils';
+
 import types from './mutation_types';
 
 export function setActiveTab({ commit }, tab) {
@@ -11,3 +13,20 @@ export function setEndpoints({ commit }, endpoints) {
 export function setMrMetadata({ commit }, metadata) {
   commit(types.SET_MR_METADATA, metadata);
 }
+
+export function fetchMrMetadata({ dispatch, state }) {
+  if (state.endpoints?.metadata) {
+    axios
+      .get(state.endpoints.metadata)
+      .then((response) => {
+        dispatch('setMrMetadata', response.data);
+      })
+      .catch(() => {
+        // https://gitlab.com/gitlab-org/gitlab/-/issues/324740
+        // We can't even do a simple console warning here because
+        // the pipeline will fail. However, the issue above will
+        // eventually handle errors appropriately.
+        // console.warn('Failed to load MR Metadata for the Overview tab.');
+      });
+  }
+}

spec/frontend/mr_notes/stores/actions_spec.js

+import MockAdapter from 'axios-mock-adapter';
+
 import testAction from 'helpers/vuex_action_helper';
-import { setEndpoints, setMrMetadata } from '~/mr_notes/stores/actions';
+import axios from '~/lib/utils/axios_utils';
+
+import { setEndpoints, setMrMetadata, fetchMrMetadata } from '~/mr_notes/stores/actions';
 import mutationTypes from '~/mr_notes/stores/mutation_types';
 
 describe('MR Notes Mutator Actions', () => {
@@ -42,4 +46,48 @@ describe('MR Notes Mutator Actions', () => {
       );
     });
   });
+
+  describe('fetchMrMetadata', () => {
+    const mrMetadata = { meta: true, data: 'foo' };
+    const state = {
+      endpoints: {
+        metadata: 'metadata',
+      },
+    };
+    let getSpy;
+    let mock;
+
+    beforeEach(() => {
+      getSpy = jest.spyOn(axios, 'get');
+      mock = new MockAdapter(axios);
+
+      mock.onGet(state.endpoints.metadata).reply(200, mrMetadata);
+    });
+
+    afterEach(() => {
+      getSpy.mockRestore();
+      mock.restore();
+    });
+
+    it('should fetch the data from the API', async () => {
+      await fetchMrMetadata({ state, dispatch: () => {} });
+
+      expect(axios.get).toHaveBeenCalledWith(state.endpoints.metadata);
+    });
+
+    it('should set the fetched data into state', () => {
+      return testAction(
+        fetchMrMetadata,
+        {},
+        state,
+        [],
+        [
+          {
+            type: 'setMrMetadata',
+            payload: mrMetadata,
+          },
+        ],
+      );
+    });
+  });
 });