Add 'inventory_hostname' to the jail plugin documentation (#6118)
This fixes the following warning on FreeBSD:
[WARNING]: The "jail" connection plugin has an improperly configured
remote target value, forcing "inventory_hostname" templated value
instead of the string
(cherry picked from commit 9a97bc7c11)
Co-authored-by: Giacomo Olgeni <olgeni@olgeni.com>
