Allow committing scheduled issue assignees to JIRA

Currently when committing a live plan, issue assignments made by the scheduling algorithm are not saved to JIRA's assignee field. This suggestion is to add the ability to update the assignee on issues when committing.

Note that manual issue assignments can be committed to JIRA, if the Commit issue assignee plan configuration option is enabled. This suggestion is about committing automatic/scheduled assignments to JIRA.