Show funds in pending htlcs as `pending` in `getbalance`

[kilrau]

Follow-up of https://github.com/ExchangeUnion/xud/pull/1680, needed for https://github.com/ExchangeUnion/xud/issues/1673: since we now treat a swap as atomically completed upon reaching PreimageResolved from maker's perspective, we should show balance that is currently in swap recovery with xud trying to claim the htlc but still didn't manage to do so (and might go on-chain at some point) as pending in getbalance.

In other words: in addition to new pending channels, any balance in pending htlc should show as pending under getbalance.

Currently this balance isn't shown anywhere and the user would see a successfully completed swap, deducted outgoing asset balance, but nothing added for the incoming asset's balance (where is my money?).

[kilrau]

For example funds from this failed swap don't show anywhere in xud:

lndbtc:

            "pending_htlcs": [
                {
                    "incoming": true,
                    "amount": "10000",
                    "hash_lock": "928a7b6caf95b590b78db560db427dd6731a2f208c11b394ede420599ba3e927",
                    "expiration_height": 640526
                }
            ],

connext:

bash-5.0# curl -H 'Content-Type: application/json' http://0.0.0.0:5040/hashlock-status/0x928a7b6caf95b590b78db560db427dd6731a2f208c11b394ede420599ba3e927/0x0000000000000000000000000000000000000000 | jq
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   438  100   438    0     0    863      0 --:--:-- --:--:-- --:--:--   863
{
  "senderIdentifier": "indraABC",
  "receiverIdentifier": "indraABC",
  "assetId": "0x0000000000000000000000000000000000000000",
  "amount": "100000000000000",
  "lockHash": "0x928a7b6caf95b590b78db560db427dd6731a2f208c11b394ede420599ba3e927",
  "status": "PENDING",
  "preImage": "0x0000000000000000000000000000000000000000000000000000000000000000",
  "expiry": "10517875"
}

[ghost]

Getting the amount of funds locked up via /hashlock-status endpoint might not be the best solution because of the complexity it adds on xud level to track the payments. Perhaps connext client can consider displaying this information in the response of /balance endpoint? Or a more general /getinfo endpoint?

[kilrau]

Agree. Wdyt? @ArjunBhuptani

[kilrau]

Also, currently the connext client doesn't seem to account for funds locked in an htlc. The balance reported is still the same. We propose to add 4 different balances to the connext client (either in one /balance endpoint or 4 different endpoints ):

1. off-chain
2. off-chain pending
3. on-chain
4. on-chain pending

[kilrau]

Moved this to P2 since we are depending on changes from connext side: https://github.com/connext/rest-api-client/issues/66