HAProxy and OPNSense HAProxy add-on added to the proxy guides. (#24671)

* Include HAProxy example in reverse proxy guide

Added HAProxy configuration example for reverse proxy setup.

* Revise HAProxy config and add OPNSense guide

Updated HAProxy configuration details and added a guide for OPNSense HAProxy add-on setup.

* Revise HAProxy configuration steps in guide

Updated the step-by-step guide for configuring HAProxy on OPNSense, ensuring clarity and consistency in instructions.

* Update note on port 443 request forwarding

Clarified note about forwarding requests on port 443 and provided guidance on creating rules and conditions for multiple websites.

* Fix proxy mode description and bind command typo

Corrected the proxy mode description from Layer 7 to Layer 4 and fixed a typo in the bind command.

* Clarify Layer 4 proxy configuration details

Added note about changing hdr(host) to req.ssl_sni for TCP traffic.

docs/docs/guides/reverse_proxy.md

@@ -45,6 +45,8 @@ There are many solutions available to implement reverse proxies and the communit
 - [Nginx](#nginx-reverse-proxy)
 - [Traefik](#traefik-reverse-proxy)
 - [Caddy](#caddy-reverse-proxy)
+- [HAProxy](#haproxy)
+- [OPNSense HAProxy Add-on](#opnsense-haproxy-add-on)
 
 ## Apache2 Reverse Proxy
 
@@ -218,3 +220,68 @@ frigate.YOUR_DOMAIN.TLD {
 }
 
 ```
+
+## HAProxy
+
+This example is for a pure haproxy installation on a dedicated host. It assumes you have already combined the certificate parts in de cert file.
+
+The frontend config:
+```# Public Service: SSLSecured (Frigate)
+frontend SSLSecured
+    bind XXX.XXX.XXX.XXX:443 ssl crt /etc/haproxy/certs/frigate.cert
+    mode http
+    option http-keep-alive
+    default_backend NVR
+
+    # CONDITION: NVR
+    acl acl_frigate hdr(host) -i nvr.example.video
+
+    # RULE: NVR
+    use_backend NVR if acl_frigate
+```
+
+The backend config:
+```# Backend Pool: NVR (Frigate)
+backend NVR
+    mode http
+    balance source
+    # stickiness
+    stick-table type ipv4 size 50k expire 30m  
+    stick on src
+    http-reuse safe
+    server Frigate XXX.XXX.XXX.XXX:8971
+```
+The above config is created for a Layer 7 proxy (application layer, in this case http), if streaming the camera feeds are a little spotty or somewhat unstable, you can try to change the *mode* from http to tcp in both the frontend and backend config, which sets up a Layer 4 proxy (proxy by protocol). Make sure you change hdr(host) to req.ssl_sni in the frontend Condition to make the host based condition work on tcp traffic. 
+
+## OPNSense HAProxy add-on
+
+This guide is for the OPNSense firewall add-on *os-haproxy* and is configured and tested on version 5.1 of the add-on on OPNSense 26.7.
+The guide starts where you are already done setting up the system, *have a certificate added to the certificate store* and *installed the plugin/add-on*.
+
+Step by step plan:
+1. Go to Services -> HAProxy, click on Settings;
+2. Add a Real Server under *Real Servers*;
+3. Fill in the fields *Name or Prefix* and *Description*;
+4. set *Type* to **static**;
+5. fill in the frigate IP in the *FQDN or IP* field;
+6. under *Common Options* fill *Port* with the port number for your Frigate (e.g. 8971) and
+7. Click **Save** to store this configuration.
+8. Under *Virtual Services* open *Backend Pools*;
+9. Add a *Backend Pool*;
+10. Fill in the fields *Name or Prefix* and *Description* but use something else then what you used under *Real Servers* otherwise if and when rules and conditions are needed it gets really confusing really fast, the use of them is out of the scope of this guide for a basic functioning haproxy add-on;
+11. set *Mode* to **HTTP (Layer 7)**;
+12. set *Balancing Algorithm* to **Source-IP Hash**;
+13. set *Servers* by choosing the *Real Servers* instance you added in step 2->6;
+14. Click **Save** to store this configuration.
+15. Under *Virtual Services* open *Public Services*;
+16. Add a *Public Service*;
+17. Fill in the fields *Name or Prefix* and *Description* but use something else then what you used under *Real Servers* otherwise if and when rules and conditions are needed it gets really confusing really fast, the use of them is out of the scope of this guide for a basic functioning haproxy add-on;
+18. Fill in the external address the haproxy instance will be listening on in *Listen Addresses*;
+19. set *Type* to **HTTP/HTTPS (SSL offloading)**
+20. set *Default Backend Pool* to the option carrying *the name you used in step 9*;
+21. check *Enable SSL Offloading*;
+22. Under *SSL Offloading* you set *Default certificate* to the certificate you added before you started following this guide;
+23. Click **Save** to store this configuration.
+24. Click **Apply** to reload the haproxy config on the service running.
+
+**NOTE: This will forward _ALL_ requests on port 443 to your frigate instance.** If that is not what you want or have more then one website alive behind the haproxy you will need to create a *Condition* to trigger when the right URL is used and a *Rules* rule to use the right backend under *Rules & Checks* when the condition is met. This is a useful hint for those who need it, though it is out of the scope of this guide.