Allow Microsoft Graph API integration for Incoming Mail handlers (JSM) using the client credentials flow

Right now, with the implementation of the feature request JSDSERVER-12419, Jira uses the authorization code flow when integrating with MS Graph API for incoming mail handlers. We would like Jira to use the client credentials flow instead.

This is important because some organizations cannot use delegated permissions and they need to use the application permissions instead. This way, no user credentials are involved and the flow would be based on tokens only.