Add comments for all the nftable::rules entries

[traylenator]

For each nftable::rule this adds an extra concat fragment to
add a comment containing the name and order number for the rule.

The motivation here is to make the mapping from resulting rules back
to puppet code more obvious. When adding a new rule it should be more
obvious to understand what order to choose.

An example resulting table ends up reading as:

# Start of fragment order:00 default_in header
chain default_in {
#   Start of fragment order:50 rulename:default_in-dhcpv6_client
  ip6 saddr fe80::/10 ip6 daddr fe80::/10 udp sport 547 udp dport 546 accept
#   Start of fragment order:50 rulename:default_in-ssh
  tcp dport {22} accept
#   Start of fragment order:90 rulename:default_in-drop_broadcasts
  meta pkttype broadcast counter drop
# Start of fragment order:99 default_in footer
}

In addition there is a new test nftables::rule. This includes
a pending test since I would assume setting source and content
on a rule should be an error however this currently not the case.

[traylenator]

To add I did consider using the comment 'rule name order' within the rules but it is less obvious what to do with multline contents or source => specifying rules.

Happy to switch to prefixing rules with comments rather than extra fragments but the input for content might have to be stricter.

content => "\nruleA\nruleB\n"

should probably be blocked as should

content => "comment 'my comment" myrule"

since the double comment causes problems.

[nbarrientos]

Happy to switch to prefixing rules with comments rather than extra fragments but the input for content might have to be stricter.

An advantage of using built-in comments is that they show up when executing nft list ruleset which might be handy.