Supporting RHEL type in supported_dists to support Python > 3.7

[CoolZeroNL]

RHEL 8 is using rhel as ID, so adding support for that in the list.

The function platform.dist & platform.linux_distribution are been removed in python 3.7. So the DSC will use the Fallback to use /etc/os-release. This is working fine, only that RHEL is using a other name as is then is listed in the suppored_list

# cat /etc/os-release 

NAME="Red Hat Enterprise Linux"
VERSION="8.6 (Ootpa)"
ID="rhel"
ID_LIKE="fedora"
VERSION_ID="8.6"

Issue related: #1612

[CoolZeroNL]

@Bhargava-Chary-Chollaty can u review ?