Document how to configure source-based routing for MetalLB

[kvaps]

While Talos Linux itself does not support setting source-based routing, we have to provide the information how to configure it using DaemonSet.

We have to add reference on article https://blog.aenix.io/configuring-routing-for-metallb-in-l2-mode-7ea26e19219e, and configuration like this:

---
apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: routes
  namespace: cozy-metallb
spec:
  selector:
    matchLabels:
      app: routes
  template:
    metadata:
      labels:
        app: routes
    spec:
      hostNetwork: true
      containers:
      - name: routes
        image: alpine
        command:
        - /bin/sh
        - -c
        args:
        - |
          set -xe
          ip_rule_replace() {
            ip rule del $@ || true
            ip rule add $@
          }

          # Setup custom routing table
          ip route replace 1.2.3.0/24 dev bond0.100 table 100
          ip route replace default via 1.2.3.4 table 100

          # Setup policy based routing
          ip_rule_replace from 1.2.3.0/24 lookup 100
          ip_rule_replace from 1.2.3.0/24 to 10.244.0.0/16 lookup main

          exec sleep infinity
        securityContext:
          privileged: true
      terminationGracePeriodSeconds: 0
      tolerations:
      - operator: Exists

upstream issues:

• Support for routing rules and tables siderolabs/talos#7184
• Support source-based routing siderolabs/talos#8738