feat(rpc): reserved order amount for TradingLimits

[sangaman]

This exposes the amounts reserved for open orders on the TradingLimits call and subtracts reserved amounts from the maxSell and maxBuy values returned by the call.

It also removes reserved order amounts from GetBalance - reversing #1584.

The logic to calculate max sell and buys is as follows:

1. Sum up all outbound and inbound balances across all channels, as well as the maximum balances for a single channel, as we still aren't expecting to use multi-path payments. For Connext there is a single channel so we only have a single inbound & outbound value per currency.

2. Subtract reserved order amounts from the total inbound and outbound balances calculated above. E.g. if we have outbound capacity of 1.2 ETH, but we have an order to sell 0.7 ETH, our max sell would be 0.5 ETH.

3. Return the smaller of the amount calculated in step 2 or the maximum single channel balance calculated in step 1.

Resolves #1678.

Example cli formatted output below, let me know if I should tweak the format or headers. I wasn't sure about the clearest way to display this info.

┌──────────┬────────────┬───────────┬───────────────────┬──────────────────┐
│ Currency │ Max Buy    │ Max Sell  │ Reserved Outbound │ Reserved Inbound │
├──────────┼────────────┼───────────┼───────────────────┼──────────────────┤
│ BTC      │ 0.00012345 │ 0.0006789 │ 0.00075           │ 0.00025          │
└──────────┴────────────┴───────────┴───────────────────┴──────────────────┘

[raladev]

• [ ] fix sim tests
• [ ] Assertion err when placed order with amount that bigger then max buy

Trading Limits: ┌──────────┬──────────┬───────────┬───────────────────┬──────────────────┐ │ Currency │ Max Buy │ Max Sell │ Reserved Outbound │ Reserved Inbound │ ├──────────┼──────────┼───────────┼───────────────────┼──────────────────┤ │ BTC │ 0.781 │ 1.0809095 │ 0 │ 0 │ ├──────────┼──────────┼───────────┼───────────────────┼──────────────────┤ │ LTC │ 4.899638 │ 4.9 │ 0 │ 0 │ └──────────┴──────────┴───────────┴───────────────────┴──────────────────┘ simnet > sell 4 LTC/BTC 0.25 1 remaining 4 LTC entered the order book as 06d2a270-0ee1-11eb-af7c-f51a32600023 no matches found simnet > tradinglimits Error: 13 INTERNAL: Assertion failed simnet > getbalance

Balance: ┌──────────┬───────────────┬───────────────────────────────┬────────────────────────────┐ │ Currency │ Total Balance │ Wallet Balance (Not Tradable) │ Channel Balance (Tradable) │ ├──────────┼───────────────┼───────────────────────────────┼────────────────────────────┤ │ BTC │ 1.19943114 │ 0.09952164 │ 1.0999095 │ ├──────────┼───────────────┼───────────────────────────────┼────────────────────────────┤ │ LTC │ 5 │ 0 │ 5 │ └──────────┴───────────────┴───────────────────────────────┴────────────────────────────┘ simnet >