(maint) Add to supported platform list

This commit adds to the list of officially supported platform. My
rationale for adding Centos/RHEL 8 is because of this change: puppetlabs#926
My rationale for adding SLES is because of this change: puppetlabs#591

And I've also added Alma, Amazon, Oracle, Rocky and Scientific to the
list as well since they are all RedHat derivatives and would ideally be
supported alongside RHEL.

README.md

@@ -1010,12 +1010,21 @@ For information on classes, types, and functions, see the [REFERENCE.md](https:/
 
 This module supports:
 
+* AlmaLinux 8
+* Amazon Linux 2
 * Centos 7.0
+* Centos 8.0
 * Debian 8.0
 * Debian 9.0
 * Debian 10
 * Debian 11
+* OracleLinux
 * RedHat 7.0 - limited support available
+* RedHat 8.0
+* Rocky 8
+* ScientificLinux 7
+* SLES 12
+* SLES 15
 * Ubuntu 18.04
 * Ubuntu 20.04
 * Ubuntu 22.04