Provide new defined resources for managing pg_hba.conf

This patch provides a more advanced way of managing pg_hba rules, by providing a
defined resource to manage a pg_hba file, and a defined resource for managing
rules within such a file (pg_hba_rule).

These new resources are wrappers around ripinaar-concat, and utilise file
assemblies instead of a template to compose the pg_hba.conf file.

I've provided a function that interprets the old ip4|6acl arrays and converts
them to this new format for backwards compatibility as well.

I slightly reformatted our documentation to allow for better documentation of
defined resources in 'Usage' as well, and provided examples of how to use this
new resource.

This hopefully should go a long way to solving the PR's related to lack of full
functionality for pg_hba.conf.

Signed-off-by: Ken Barber <ken@bob.sh>