Fixes #37733 - Add audits of ansible role changes on hosts

This records audits when ansible role is added to a host or removed from
a host.

Defining the `to_label` method is necessary so the name of host ansible
role is shown in the format `role / host` rather than `id / host`.

app/models/host_ansible_role.rb

@@ -2,10 +2,16 @@
 
 # Join model that hosts the connection between hosts and ansible_roles
 class HostAnsibleRole < ApplicationRecord
+  audited associated_with: :host
+
   belongs_to_host
   belongs_to :ansible_role
   acts_as_list scope: :host
 
   validates :ansible_role_id, :presence => true,
                               :uniqueness => { :scope => :host_id }
+
+  def to_label
+    ansible_role.name
+  end
 end