Set up the Follow ticket changes factory Loop

Sets up the Follow ticket changes factory Loop, which keeps Implement and Shepherd in step with people: it cancels their runs when an issue is taken back, closes the pull request when its issue ends, wakes the issues it was blocking, wakes an issue when a person answers its question, and cancels runs when a Tessl pull request closes. The issue source matches Implement and defaults to Linear. When the Implement Loop of the project starts on GitHub issues, the GitHub source uses its label over the one in the request. Either source needs the Tessl App on the project repository.