* add linkinator npm package
* add new script that uses Linkinator
* reorg the excluded links file and update comments
* replace blc artifacts with linkinator artifacts in .gitignore
* update the scheduled workflow to use the new script
* dismantle BLC scripts
* add workflow_dispatch event so we can test this manually
* npm uninstall broken-link-checker
* use different exit codes depending on whether broken links are found
