Description of problem:
when provisioning RHEL8 using kickstart, there is a deprecation warning displayed regarding 'ks' paramter.
this has been taken care of for RHEL9,
https://github.com/theforeman/foreman/blob/develop/app/views/unattended/provisioning_templates/snippet/kickstart_kernel_options.erb#L40-L56

However, we could include RHEL8 in the conditional too to prevent the warning from being displayed.

Version-Release number of selected component (if applicable):
6.14.0

Steps to Reproduce:
try to kickstart provision a RHEL8 host (make sure the `kickstart_kernel_options` template is used)

Actual results:
Warning just after the anaconda installer is initialized

Expected results:
no deprecation warnings

Additional info: