Apply a specific label in non-critical error cases for team triage

[mattreid]

Came up during discussion of #147

It could be valuable in certain situations for sync2jira to help users identify issues in bulk that may need more attention. Adding a comment on an issue helps in the moment, but doesn't provide a means to find all such issues from a JQL query/dashboard. One way this could be accomplished is with a specific label.

As an example, I could see this helping a team rely on that label to identify a triage list of all issues that may need more attention (labels to identify the issue type were ambiguous and the issue was synced using the first value, etc). Ideally, sync2jira should be pretty hands off, so teams aren't splitting their attention between two systems frequently, but that makes it even more valuable to quickly and easily know where attention may be needed.