Add consistency to Omniauth keys in secrets.yml.example

The keys to configure Omniauth for WordPress were only added
to the production environment, so we unified all the keys across
the staging and preproduction environments.

config/secrets.yml.example

@@ -78,6 +78,15 @@ staging:
     #
     # Currently you can overwrite SMTP, SMS, manager, microsoft API,
     # HTTP basic, twitter, facebook, google, wordpress and security settings.
+  twitter_key: ""
+  twitter_secret: ""
+  facebook_key: ""
+  facebook_secret: ""
+  google_oauth2_key: ""
+  google_oauth2_secret: ""
+  wordpress_oauth2_key: ""
+  wordpress_oauth2_secret: ""
+  wordpress_oauth2_site: ""
   <<: *maps
   <<: *apis
 
@@ -129,6 +138,9 @@ preproduction:
   facebook_secret: ""
   google_oauth2_key: ""
   google_oauth2_secret: ""
+  wordpress_oauth2_key: ""
+  wordpress_oauth2_secret: ""
+  wordpress_oauth2_site: ""
   <<: *maps
   <<: *apis