inject localRoots in P2P topology when booting the node

[robinboening]

Currently, when enabling P2P mode, the topology-p2p template is copied over and used as is. The template does not include any localRoots and therefore the relay running in P2P mode would not know about the block producer unless the information is added manually.

I suggest we allow to inject node information as we do with NODE_TOPOLOGY for non-P2P mode. Maybe we could use the same env variable for both modes.

---

Current template looks like this

{
  "localRoots": [
    {
      "accessPoints": [],
      "advertise": false,
      "valency": 1
    }
  ],
  "publicRoots": [
    {
      "accessPoints": [
        {
          "address": "relays-new.cardano-mainnet.iohk.io",
          "port": 3001
        }
      ],
      "advertise": false
    }
  ],
  "useLedgerAfterSlot": 84916732
}

but it when it is parsed by the cardano-node the final topology-p2p.json file should look like this

{
  "localRoots": [
    { "accessPoints": [
        { "address": "my-blockproducer.io", "port": 3000 }
      ]
      , "advertise": false
      , "valency": 1
    }
  ]
, "publicRoots" : [
    { "accessPoints": [
        { "address": "relays-new.cardano-mainnet.iohk.io", "port": 3001 }
      ]
      , "advertise": true
      , "valency": 1
    }
  ]
, "useLedgerAfterSlot": 0
}