feat(worker): convert 'repository/onboarding' to typescript (#4433)

lib/config/common.ts

lib/manager/common.ts

lib/workers/repository/onboarding/branch/check.ts

lib/workers/repository/onboarding/branch/config.ts

lib/workers/repository/onboarding/branch/create.ts

lib/workers/repository/onboarding/branch/index.ts

lib/workers/repository/onboarding/branch/rebase.ts

lib/workers/repository/onboarding/pr/base-branch.ts

lib/workers/repository/onboarding/pr/config-description.ts

lib/workers/repository/onboarding/pr/errors-warnings.ts

lib/workers/repository/onboarding/pr/index.ts

lib/workers/repository/onboarding/pr/pr-list.ts

test/config/migration.spec.ts

test/config/validation.spec.ts

test/workers/repository/onboarding/pr/index.spec.js