Added media inliner service scaffolding

refs https://github.com/TryGhost/Toolbox/issues/524

- This is groundwork to build up on when adding media inlining functionality. This service will be used by the API to trigger post's content processing and media inlining.

ghost/core/core/boot.js

@@ -310,6 +310,7 @@ async function initServices({config}) {
     const tagsPublic = require('./server/services/tags-public');
     const postsPublic = require('./server/services/posts-public');
     const slackNotifications = require('./server/services/slack-notifications');
+    const mediaInliner = require('./server/services/media-inliner');
 
     const urlUtils = require('./shared/url-utils');
 
@@ -346,7 +347,8 @@ async function initServices({config}) {
         comments.init(),
         linkTracking.init(),
         emailSuppressionList.init(),
-        slackNotifications.init()
+        slackNotifications.init(),
+        mediaInliner.init()
     ]);
     debug('End: Services');
 

ghost/core/core/server/services/media-inliner/service.js

@@ -0,0 +1,16 @@
+module.exports = {
+    async init() {
+        const debug = require('@tryghost/debug')('mediaInliner');
+
+        this.api = {
+            // @NOTE: the inlining should become an offloaded job
+            // startMediaInliner: mediaInliner.inlineMedia
+            startMediaInliner: () => {
+                debug('[Inliner] Starting media inlining job');
+                return {
+                    status: 'success'
+                };
+            }
+        };
+    }
+};