Have an option to not update existing worklogs

[mmaslowskicc]

I want to add new worklogs without updating existing ones in the destination JIRA so I'm sure that descriptions of existing worklogs are not changed due to jira_timemachine changes while jira_timemachine queries source Tempo-less JIRA for more days of worklogs than contain the new worklogs (e.g. due to some issues not being marked as updated when the newest worklog was added).

This should keep writing what changes would be applied or not.