copy-custom-certificate hook does not encode cert data to base64

[marriva]

./common-hooks/copy-custom-certificate/hook.go does not encode cert data to base64, so lib-helm's template helm_lib_module_https_copy_custom_certificate does not work correctly, so we need to use workaround https://github.com/deckhouse/virtualization/blob/main/templates/custom-certificate.yaml