Description of problem:
When system is not registered, then DNF plugin subscription-manager print warning with suggestion to use subscription-manager for registration. When "rhc" is installed, then this tool should be also suggested as optional CLI tool for registration.

Version-Release number of selected component (if applicable):
[root@rhel9 ~]# subscription-manager version
server type: Red Hat Subscription Management
subscription management server: 4.2.15-1
subscription management rules: 5.43
subscription-manager: 1.29.33.1-1.el9_2

How reproducible:
100%

Steps to Reproduce:
1. Try to run dnf command on not registered system, where "rhc" is also installed:

[root@rhel9 ~]# dnf install zsh

Actual results:
...
This system is not registered with an entitlement server. You can use subscription-manager to register.
...

Expected results:

...
This system is not registered with an entitlement server. You can use "rhc" or "subscription-manager" to register.
...

Additional info:
When "rhc" is not install, then message should be still the same.