bgp: Add command for retrieving bgp routes

[rastislavs]

This change introduces a new BGP status command: cilium bgp routes. BGP routes can be retrieved from either all or a specific node; in json or summary formats.

The implementation follows the existing patterns of the cilium bgp peers command and mirrors the cilium-dbg bgp routes CLI added in cilium/cilium#27182 .

The change also adds an alias for the existing cilium bgp peers command (cilium bgp neighbors) to align with cilium-dbg.

Vendor updates as part of the change is mostly due to the necessary BGP packet types from GoBGP.

Examples:

Help:

$ cilium bgp routes -h                                                                                                                                   
Lists BGP routes from all nodes in the cluster - requires cilium >= v1.15.0

Usage:
  cilium bgp routes <available | advertised> <afi> <safi> [vrouter <asn>] [peer|neighbor <address>] [flags]

Examples:
  Get all IPv4 unicast routes available:
    cilium bgp routes available ipv4 unicast

  Get all IPv6 unicast routes available for a specific vrouter:
    cilium bgp routes available ipv6 unicast vrouter 65001

  Get IPv4 unicast routes advertised to a specific peer:
    cilium bgp routes advertised ipv4 unicast peer 10.0.0.1

Flags:
      --agent-pod-selector string   Label on cilium-agent pods to select with (default "k8s-app=cilium")
  -h, --help                        help for routes
      --node string                 Node from which BGP routes will be fetched, omit to select all nodes
  -o, --output string               Output format. One of: json, summary (default "summary")
      --wait-duration duration      Maximum time to wait for result, default 1 minute (default 1m0s)

Global Flags:
      --context string     Kubernetes configuration context
  -n, --namespace string   Namespace Cilium is running in (default "kube-system")

Simplest use:

$ cilium bgp routes                                                                                                                                                                     
(Defaulting to `available ipv4 unicast` routes, please see help for more options)

Node                              VRouter   Prefix        NextHop    Age   Attrs
bgp-cplane-dev-v4-control-plane   65001     10.1.0.0/24   0.0.0.0    55s   [{Origin: i} {Nexthop: 0.0.0.0}]                          
                                  65001     10.1.1.0/24   10.0.1.1   55s   [{Origin: i} {AsPath: 65000 65002} {Nexthop: 10.0.1.1}]   
bgp-cplane-dev-v4-worker          65002     10.1.0.0/24   10.0.2.1   55s   [{Origin: i} {AsPath: 65000 65001} {Nexthop: 10.0.2.1}]   
                                  65002     10.1.1.0/24   0.0.0.0    55s   [{Origin: i} {Nexthop: 0.0.0.0}]                     

Advertised routes to a specific peer of a specific node:

$ cilium bgp routes advertised ipv4 unicast peer 10.0.2.1 --node bgp-cplane-dev-v4-worker                                                                         
Node                       VRouter   Prefix        NextHop    Age     Attrs
bgp-cplane-dev-v4-worker   65002     10.1.1.0/24   10.0.2.2   1m37s   [{Origin: i} {AsPath: 65002} {Nexthop: 10.0.2.2}] 

The same as json:

$ cilium bgp routes advertised ipv4 unicast peer 10.0.2.1 --node bgp-cplane-dev-v4-worker -o json                                                                    
{
 "bgp-cplane-dev-v4-worker": [
  {
   "paths": [
    {
     "age-nanoseconds": 138734627807,
     "family": {
      "afi": "ipv4",
      "safi": "unicast"
     },
     "nlri": {
      "base64": "GAoBAQ=="
     },
     "path-attributes": [
      {
       "base64": "QAEBAA=="
      },
      {
       "base64": "QAIGAgEAAP3q"
      },
      {
       "base64": "QAMECgACAg=="
      }
     ]
    }
   ],
   "prefix": "10.1.1.0/24",
   "router-asn": 65002
  }
 ]
}

[harsimran-pabla]

Thank you, LGTM.

[derailed]

@rastislavs Nice work!

[derailed]

@rastislavs Thank you for the updates!

[rastislavs]

@sayboras could you please take a look at this PR? It is now missing only vendor review.

[sayboras]

LGTM ✔️