Added media inliner feature alpha flag

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

- This flag will be used to test the trigger to external media inliner job
- The Admin UI is still unclear so sticking it behind the flag for some experimentation before shipping the feature

ghost/admin/app/services/feature.js

@@ -72,6 +72,7 @@ export default class FeatureService extends Service {
     @feature('milestoneEmails') milestoneEmails;
     @feature('websockets') websockets;
     @feature('stripeAutomaticTax') stripeAutomaticTax;
+    @feature('mediaInliner') mediaInliner;
 
     _user = null;
 

ghost/admin/app/templates/settings/labs.hbs

@@ -265,6 +265,19 @@
                         </div>
                     </div>
                 </div>
+                <div class="gh-expandable-block">
+                    <div class="gh-expandable-header">
+                        <div>
+                            <h4 class="gh-expandable-title">External Media Inliner</h4>
+                            <p class="gh-expandable-description">
+                               Inline external media hotlinked in post's content.
+                            </p>
+                        </div>
+                        <div class="for-switch">
+                            <GhFeatureFlag @flag="mediaInliner" />
+                        </div>
+                    </div>
+                </div>
             </div>
         </div>
         {{/if}}

ghost/core/core/shared/labs.js

@@ -35,6 +35,7 @@ const BETA_FEATURES = [
 
 const ALPHA_FEATURES = [
     'urlCache',
+    'mediaInliner',
     'lexicalEditor',
     'websockets',
     'webmentionEmails',