Added e2e test covering media inliner job start

refs https://github.com/TryGhost/Toolbox/issues/523

- The test is useful for future iterations of the response format and as a quick reference on which parameters the media inlining endpoint accepts.

ghost/core/test/e2e-api/admin/db.test.js

@@ -84,4 +84,24 @@ describe('DB API', function () {
         eventsTriggered['post.deleted'].length.should.eql(7);
         eventsTriggered['tag.deleted'].length.should.eql(1);
     });
+
+    it('Can trigger external media inliner', async function () {
+        const response = await request
+            .post(localUtils.API.getApiQuery('db/media/inline'))
+            .send({
+                domains: ['https://example.com']
+            })
+            .set('Origin', config.get('url'))
+            .set('Accept', 'application/json')
+            .expect(200);
+
+        // @NOTE: the response format is temporary for test purposes
+        //        before feature graduates to GA, it should become
+        //        a more consistent format
+        response.body.should.eql({
+            db: [{
+                status: 'success'
+            }]
+        });
+    });
 });