feat(constants): Manager Constants (#5168)

lib/constants/managers.ts

lib/manager/gradle/index.ts

lib/manager/index.ts

lib/manager/npm/extract/index.ts

lib/manager/pub/extract.ts

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

test/manager/index.spec.ts

test/manager/range.spec.ts

test/util/package-rules.spec.ts

test/workers/branch/get-updated.spec.ts

test/workers/repository/extract/manager-files.spec.ts

test/workers/repository/process/lookup/index.spec.ts