Replace steps to update the system truststore with link to RHEL docs

[aneta-petrova]

3.2. Adding new certificates in RHEL docs includes instructions to add certs to the system trustore: https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/9/html/securing_networks/using-shared-system-certificates_securing-networks#adding-new-certificates_using-shared-system-certificates

In 7.1. Configuring TLS for secure LDAP, we document the same procedure: https://docs.theforeman.org/nightly/Configuring_User_Authentication/index-katello.html#Configuring_TLS_for_Secure_LDAP_authentication

We should try looking into whether we can replace the steps on the Foreman side with a link to the RHEL docs. The RHEL docs include more details on the subject and are maintained by a dedicated team so they are more likely to receive relevant updates.