Edit label if it exists on destination with source's label

Currently right now if a label exists on the destination project it triggers the `Validation Failed` error. Maybe add an option in can pass in where it would edit the existing label at destination with the label's properties of source. So editing the label's description, color, ect with what's on soure.

Start by locating the label-copy flow and the GitHub API request that currently fails when the destination already has a label. Determine how an option should enable updating the destination label's description, color, and other properties from the source. Done means the option is documented and existing destination labels are updated without the validation error; no files or tests are named in the issue.

Written by the indexing model from the issue text.