Fix documentation to show that validators are disabled by default

[CloudoguSiebels]

In https://github.com/cloudogu/gitops-build-lib/commit/ef676df34eb798971073d6b6378a70a97d9e9a99 the validators kubeval and helmkubeval were disabled.

The README suggests that all these validators are enabled by default: https://github.com/cloudogu/gitops-build-lib/tree/main#validators