feat: helmfile manager (#5257)

docs/usage/configuration-options.md

lib/config/definitions.ts

lib/constants/managers.ts

lib/manager/helmfile/extract.ts

lib/manager/helmfile/index.ts

lib/manager/helmfile/update.ts

lib/manager/index.ts

renovate-schema.json

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

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

test/manager/helmfile/__snapshots__/update.spec.ts.snap

test/manager/helmfile/extract.spec.ts

test/manager/helmfile/update.spec.ts

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