Add example of how to integrate haproxy (#239)

* add: haproxy scripts

* add: haproxy readme

I am really bad at writing instructions.

haproxy/50-haproxy.sh

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+#!/bin/sh
+CONTAINER=haproxy
+
+# Starts a cloudflare ddns container that is deleted after it is stopped.
+# All configs stored in /mnt/data/cloudflare-ddns
+if podman container exists "$CONTAINER"; then
+  podman start "$CONTAINER"
+else
+podman run -d --net=host --restart always \
+  --name haproxy \
+  --hostname ha.proxy \
+  -v "/mnt/data/haproxy/:/usr/local/etc/haproxy/" \
+  haproxy:latest

haproxy/README.md

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+# Run haproxy on your UDM
+
+## Features
+
+1. Load balance services on your UDM, because why not?.
+2. Persists through reboots and firmware updates.
+
+## Requirements
+
+1. You have successfully setup the on boot script described [here](https://github.com/boostchicken/udm-utilities/tree/master/on-boot-script)
+2. You have to have services you want to load-balance, an example would be a multi-master k3s cluster.
+
+## Steps
+
+1. Pull your image with `podman pull docker.io/library/haproxy`.
+1. (Optional) Configure a network using the generic cni network [20-dns.conflist](../cni-plugins/20-dns.conflist) and update its values to reflect your environment
+1. Copy [50-haproxy.sh](./50-haproxy.sh) to `/mnt/data/on_boot.d/50-haproxy.sh`.
+1. Create a persistant directory and config for haproxy to use:
+
+    ```sh
+    mkdir -p /mnt/data/haproxy
+    touch /mnt/data/haproxy/haproxy.cfg
+    ```
+
+1. Add your config to `/mnt/data/haproxy/haproxy.cfg`. Each configuration is unique, so check out some resouces like [haproxy.com](https://www.haproxy.com/documentation/hapee/latest/configuration/config-sections/) for basics.
+1. Run `/mnt/data/on_boot.d/50-haproxy.sh`
+
+## Upgrading Easily (if at all)
+
+1. Edit [update-pihole.sh](./update-pihole.sh) to use the same command you used at installation (if changed).
+2. Copy the [update-pihole.sh](./update-pihole.sh) to `/mnt/data/scripts`
+3. Anytime you want to update your installation, simply run `/mnt/data/scripts/update-pihole.sh`

haproxy/update-haproxy.sh

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+podman pull haproxy
+podman stop haproxy
+podman rm haproxy
+podman run -d --net=host --restart always \
+  --name haproxy \
+  --hostname ha.proxy \
+  -v "/mnt/data/haproxy/:/usr/local/etc/haproxy/" \
+  haproxy:latest