fix: move git author logic to global worker and validate (#3410)

lib/platform/bitbucket-server/index.js

lib/platform/git/storage.js

lib/platform/github/index.js

lib/platform/github/storage.js

lib/platform/gitlab/index.js

lib/platform/gitlab/storage.js

lib/workers/global/index.js

lib/workers/global/meta.js

test/platform/git/storage.spec.js

test/platform/github/index.spec.js

test/workers/global/index.spec.js