k3s_server_post: add cilium_bgp_neighbors parameter (#579)

With the cilium_bgp_neighbors parameter it is possible to define
multiple BGP peer ASN & address pairs for Cilium.

Sample:

```
cilium_bgp_neighbors:
  - peer_address: 192.168.128.10
    peer_asn: 64512
  - peer_address: 192.168.128.11
    peer_asn: 64512
  - peer_address: 192.168.128.12
    peer_asn: 64512
```

It is possible to merge further lists with cilium_bgp_neighbors__*
parameters.

Sample:

```
cilium_bgp_neighbors__extra:
  - peer_address: 192.168.128.10
    peer_asn: 64512
cilium_bgp_neighbors:
  - peer_address: 192.168.128.11
    peer_asn: 64512
  - peer_address: 192.168.128.12
    peer_asn: 64512
```

This will result in the following list of BGP peer ASN & address pairs:

```
- peer_address: 192.168.128.10
  peer_asn: 64512
- peer_address: 192.168.128.11
  peer_asn: 64512
- peer_address: 192.168.128.12
  peer_asn: 64512
```

Signed-off-by: Christian Berendt <berendt@osism.tech>

roles/k3s_server_post/templates/cilium.crs.j2

@@ -7,6 +7,19 @@ spec: # CiliumBGPPeeringPolicySpec
  - localASN: {{ cilium_bgp_my_asn }}
    exportPodCIDR: {{ cilium_exportPodCIDR | default('true') }}
    neighbors: # []CiliumBGPNeighbor
+{% if _cilium_bgp_neighbors | length > 0 %}
+{% for item in _cilium_bgp_neighbors %}
+    - peerAddress: '{{ item.peer_address + "/32"}}'
+      peerASN: {{ item.peer_asn }}
+      eBGPMultihopTTL: 10
+      connectRetryTimeSeconds: 120
+      holdTimeSeconds: 90
+      keepAliveTimeSeconds: 30
+      gracefulRestart:
+        enabled: true
+        restartTimeSeconds: 120
+{% endfor %}
+{% else %}
     - peerAddress: '{{ cilium_bgp_peer_address + "/32"}}'
       peerASN: {{ cilium_bgp_peer_asn }}
       eBGPMultihopTTL: 10
@@ -16,6 +29,7 @@ spec: # CiliumBGPPeeringPolicySpec
       gracefulRestart:
         enabled: true
         restartTimeSeconds: 120
+{% endif %}
    serviceSelector:
       matchExpressions:
          - {key: somekey, operator: NotIn, values: ['never-used-value']}