website/integrations: Document using pfSense as Provider Integration (#2534)

* Add pfSense documentation

* add pfSense to sidebar

* Add pfsense secure setup

* rearrangement of sections for better clarity

* Add port value in unsecure setup

* change admonitions type for unsecure setup

* add `Test you setup` section

* add `Change pfSense default authentication backend` section

* Minor corrections

Co-authored-by: Danaël Giordana <danael@giordana.cc>

website/sidebarsIntegrations.js

@@ -27,6 +27,7 @@ module.exports = {
                 "services/onlyoffice/index",
                 "services/opnsense/index",
                 "services/paperless-ng/index",
+                "services/pfsense/index",
                 "services/portainer/index",
                 "services/powerdns-admin/index",
                 "services/proxmox-ve/index",