T6687: add fqdn support to nat rules. (backport #4024)

[mergify]

Change Summary

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://vyos.dev/T6687

Related PR(s)

Component(s) name

nat

Proposed changes

How to test

vyos@fqdn-nat# run show config comm | grep nat
set nat destination rule 10 destination fqdn 'vyos.dev'
set nat destination rule 10 inbound-interface name 'eth2'
set nat destination rule 10 translation address '198.51.100.55'
set system host-name 'fqdn-nat'
[edit]
vyos@fqdn-nat# sudo nft -s list table ip vyos_nat
table ip vyos_nat {
        set FQDN_nat_destination_10_d {
                type ipv4_addr
                flags interval
                elements = { 104.18.2.133, 104.18.3.133 }
        }

        chain PREROUTING {
                type nat hook prerouting priority dstnat; policy accept;
                counter jump VYOS_PRE_DNAT_HOOK
                iifname "eth2" ip daddr @FQDN_nat_destination_10_d counter dnat to 198.51.100.55 comment "DST-NAT-10"
        }

        chain POSTROUTING {
                type nat hook postrouting priority srcnat; policy accept;
                counter jump VYOS_PRE_SNAT_HOOK
        }

        chain VYOS_PRE_DNAT_HOOK {
                return
        }

        chain VYOS_PRE_SNAT_HOOK {
                return
        }
}
[edit]
vyos@fqdn-nat# sudo ps aux | grep vyos-domain
root        2928  0.6  5.1  64160 51124 ?        Ss   17:56   0:00 /usr/bin/python3 -u /usr/libexec/vyos/vyos-domain-resolver.py
vyos        3134  0.0  0.2   6332  2048 ttyS0    S+   17:57   0:00 grep vyos-domain
[edit]
vyos@fqdn-nat# 

Smoketest result

• test_firewall.py --> OK
• test_nat.py --> OK

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

---

This is an automatic backport of pull request #4024 done by [Mergify](https://mergify.com).

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