chore!(firewall): iptables logger level is set at FIREWALL_IPTABLES_LOG_LEVEL

- firewall log level is still fully controlled by `LOG_LEVEL`
- iptables log level defaults to `info` even if global log level is `debug` to minimize the amount of debug logs
- iptables log level is only set to debug if retro-compatible `FIREWALL_DEBUG=on` or if `FIREWALL_IPTABLES_LOG_LEVEL=debug`

internal/configuration/settings/settings_test.go

@@ -62,7 +62,9 @@ func Test_Settings_String(t *testing.T) {
 |       ├── Block ads: no
 |       └── Block surveillance: yes
 ├── Firewall settings:
-|   └── Enabled: yes
+|   ├── Enabled: yes
+|   └── Iptables settings:
+|       └── Log level: INFO
 ├── Log settings:
 |   └── Log level: INFO
 ├── Health settings: