Add support for Oauth2 (3LO) for all JSD REST API endpoints

Issue Summary

Currently not all the JSD REST API endpoints support Oauth2. Indeed, while for many of them you can see that the Oauth scope is documented: 

OAuth scopes required:  manage:servicedesk-customer

For others (like the below ones) this is missing and an error is returned while trying to call them using 3LO:

• Get info /rest/servicedeskapi/info
• Get articles /rest/servicedeskapi/knowledgebase/article
• Get all request types /rest/servicedeskapi/requesttype

Steps to Reproduce

1. Send a REST API request to the  /rest/servicedeskapi/requesttype endpoint using 3LO authorization

Expected Results

A list of request types is returned

Actual Results

The below error is returned:

{"errorMessages":["OAuth 2.0 is not enabled for this method."]}

Workaround

Use any other authentication method for the time being.