Add support for RHEL 8 and Puppet 7

[GertjanBijl]

Current supported OS versions and Puppet versions are behind. We would like to be able to upgrade to RHEL 8 and Puppet 7.

[lvicainne]

Hi !
For sure, an upgrade would be welcome :)

[GertjanBijl]

I think I will be able to create a pull request for RHEL8 support, as I already have that available, but as we haven't upgraded to Puppet 7 anywhere yet, I really cannot test that.