fix the api docs generation

Every time that we run `rake canvas:compile_assets` task, the file
data_service_canvas_logged.md changes, where the brake line is removed
from the body attribute.

This behavior does not occurs while using  the `rake doc:api` task.

After some investigation, we notice that to solve this issue we need to:
* load the json initializer (config/initializers/json) at the `doc:api` task;
* format the JSON file properly;
* fix the data_service_canvas_logged.md file to the correct version;

closes INTEROP-6346
flag=none

test plan:
* checkout this patch;
* run rake canvas:compile_assets and check that the file
data_service_canvas_logged.md doesn't change anymore;
* run rake doc:api and check that the file
data_service_canvas_logged.md doesn't change anymore;

Change-Id: I8cb1e3cb5d9527205827fa25b74e6da3319f65ab
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/253036
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Robin Kuss <rkuss@instructure.com>
Reviewed-by: Xander Moffatt <xmoffatt@instructure.com>
QA-Review: Robin Kuss <rkuss@instructure.com>
Product-Review: Wagner Goncalves <wagner.goncalves@instructure.com>

doc/api/data_services/json/canvas/event-types/logged_out.json

@@ -2,8 +2,7 @@
   "name": "logged_out",
   "definition": "The event is emitted anytime an end user logs out of Canvas",
   "trigger": "Triggered when a user has logged out.",
-  "schema": {
-  },
+  "schema": {},
   "examples": [
     {
       "payload": {
@@ -28,9 +27,8 @@
           "user_login": "oxana@example.com",
           "user_sis_id": "456-T45"
         },
-        "body": {
-        }
+        "body": {}
       }
     }
   ]
-}
+}

doc/api/data_services/md/dynamic/data_service_canvas_logged.md

@@ -85,8 +85,7 @@ Logged
     "user_login": "oxana@example.com",
     "user_sis_id": "456-T45"
   },
-  "body": {
-  }
+  "body": {}
 }
 ```
 

lib/tasks/docs.rake

@@ -1,6 +1,7 @@
 begin
   require 'yard'
   require 'yard-appendix'
+  require 'config/initializers/json'
 
 namespace :doc do
   DOC_DIR     = File.join(%w[public doc api])