selinux policy: add the right context for org.freeipa.server.trust-enable-agent
    
    This commit sets the system_u:object_r:ipa_helper_exec_t:s0 context to the
    oddjob script org.freeipa.server.trust-enable-agent.
    Without this context, oddjob cannot launch the command
    /usr/libexec/ipa/oddjob/org.freeipa.server.trust-enable-agent
    when ipa-adtrust-install --add-agents is run with SElinux enforcing.
    
    Related: https://pagure.io/freeipa/issue/7600
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>