Add optional input for selectively opting-out of sync

[amccall-eigt]

New Input: sync-ignore-labels Required: No

Use Case: We would like to be able to add specific labels at PR creation that do not interact with the labeler labels. This is particularly useful for opting out of build automation that runs based on assigned labels.

Test case has been added to validate the behavior and all test cases are passing.

README.md has been updated to reflect new input.