Added body parser to web/api/v2 express app

refs #9866

- req.body is undefined if we don't use the body parser
- the content API only offers "fetch" endpoints, but if a component/module in Ghost relies on req.body being present, it can crash
- e.g. the authentication service checks for the existence of client_id + client_secret in req.query or req.body
- we could theoretically change it from `if (!req.body.client_id` to `if (req.body && !req.body.client_id)`, but that makes the code very hard to read + maintain
- we will use the body parser for the content API now
- req.body will be {}

core/server/web/api/v2/content/app.js

@@ -1,5 +1,6 @@
 const debug = require('ghost-ignition').debug('api');
 const boolParser = require('express-query-boolean');
+const bodyParser = require('body-parser');
 const express = require('express');
 const shared = require('../../../shared');
 const routes = require('./routes');
@@ -10,6 +11,9 @@ module.exports = function setupApiApp() {
 
     // API middleware
 
+    // @NOTE: req.body is undefined if we don't use this parser, this can trouble if components rely on req.body being present
+    apiApp.use(bodyParser.json({limit: '1mb'}));
+
     // Query parsing
     apiApp.use(boolParser());