feat(cdnurl): Add CDNJS support (#5254)

docs/usage/configuration-options.md

lib/config/definitions.ts

lib/constants/managers.ts

lib/datasource/cdnjs/index.ts

lib/manager/cdnurl/extract.ts

lib/manager/cdnurl/index.ts

lib/manager/cdnurl/update.ts

lib/manager/index.ts

renovate-schema.json

test/config/__snapshots__/validation.spec.ts.snap

test/manager/cdnurl/__snapshots__/extract.spec.ts.snap

test/manager/cdnurl/_fixtures/sample.txt

test/manager/cdnurl/extract.spec.ts

test/manager/cdnurl/update.spec.ts

...rkers/repository/extract/__snapshots__/index.spec.ts.snap