Service desk sometimes treats Connect addon users as external customers

If an administrator removes a Connect addon user from all the groups that have use permissions in JIRA, `RedirectExternalCustomerToPortalFilter` will redirect all the REST calls done by the Connect addon to the customer portal.

It would be possible to detect if the user is a connect addon user, and skip the redirect. (Atlassian connect does its own scope based permission check, so this is not going to cause any problems)

See https://ecosystem.atlassian.net/browse/AC-1416.