Allow configuring the timeout for Service Desk mail handlers

As of JSD 4.3 it is not possible to set the timeout for Service Desk mail handlers, and this can give issues, especially with certain email services like Office365.

There was an issue in the past tracked in the bug report JSDSERVER-793 and at the time that was increased from 5 to 60 seconds, but it seems either a new adjustment might be required or to allow administrators to configure it.

This issue has been observed to happen on large mailbox with GBs of messages in Office 365 / Exchange Server. Reducing the mailbox size prevents this problem from happening. We recommend adding a rotation in mailboxes to automatically archive messages older than a certain date so the inbox folder listing is faster.