[CBR-461] Improve diagnostic for NotEnoughMoney error

[KtorZ]

Description

When computing fees or making a transaction, it could happen that funds
are currently "locked" out because selected in a pending transaction. In
such case, the UTxO can't be spent until the transaction has been
accepted by (at least) a node. The API currently returns a
NotEnoughMoney error in such case, whereas the total balance (as
returned by /api/v1/wallets/{walletId} endpoint) might show enough
funds.

This refines a bit the NotEnoughMoney error to make the reason
of failure clearer without breaking (too much) the existing API.

NOTE: There's one "expected" failing integration test which actually shed the light on a newly discovered bug (0 fee transaction).

Linked issue

[CBR-461]

Type of change

• 🐞 Bug fix (non-breaking change which fixes an issue)
• 🛠 New feature (non-breaking change which adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)
• 🏭 Refactoring that does not change existing functionality but does improve things like code readability, structure etc
• 🔨 New or improved tests for existing code
• ⛑ git-flow chore (backport, hotfix, etc)

Developer checklist

• I have read the style guide document, and my code follows the code style of this project.
• If my code deals with exceptions, it follows the guidelines.
• I have updated any documentation accordingly, if needed. Documentation changes can be reflected in opening a PR on cardanodocs.com, amending the inline Haddock comments, any relevant README file or one of the document listed in the docs directory.
• CHANGELOG entry has been added and is linked to the correct PR on GitHub.

Testing checklist

• I have added tests to cover my changes.
• [ ] All new and existing tests passed.

QA Steps

Screenshots (if available)

[KtorZ]

Integration tests failing as "expected":

  integration/Util.hs:129:5: 
  1) Transactions fails if you can't cover fee with a transaction
       Falsifiable (after 1 test):
       
       predicate failed on: Right (Transaction {txId = AbstractHash 9459bb25a09439a0337857db0e2d3f95bf240a0a1608d60b9616072da4873ad6, txConfirmations = 0, txAmount = Coin {getCoin = 42}, txInputs = PaymentDistribution {pdAddress = Address {addrRoot = AbstractHash 42a18f1ee2cbbf37aad3370b27e43861c5330931c310157d75462dd7, addrAttributes = Attributes { data: AddrAttributes {aaPkDerivationPath = Just (HDAddressPayload {getHDAddressPayload = "\ENQ\SO{ \SI\RS\222\212\193\255\192c\166\200\v\204\182\240\201\161\213M\166V\134\160\172\212"}), aaStakeDistribution = BootstrapEraDistr} }, addrType = ATPubKey}, pdAmount = Coin {getCoin = 42}} :| [], txOutputs = PaymentDistribution {pdAddress = Address {addrRoot = AbstractHash f4cbe4cdeb6f727dd973b130c1233753415b69a601a3509c692eff45, addrAttributes = Attributes { data: AddrAttributes {aaPkDerivationPath = Just (HDAddressPayload {getHDAddressPayload = "\137\229\DC3(\US\229rmFE9\EOT+\129\GS\218w\166baK\156\213\EOT<\192-\147"}), aaStakeDistribution = BootstrapEraDistr} }, addrType = ATPubKey}, pdAmount = Coin {getCoin = 42}} :| [], txType = ForeignTransaction, txDirection = OutgoingTransaction, txCreationTime = 1538569020551488, txStatus = Applying})

Investigating in [CBR-462]

[adinapoli-iohk]

LGTM.

[adinapoli-iohk]

Reminds me also of https://iohk.myjetbrains.com/youtrack/issue/CBR-449, heh.

[KtorZ]

Whoops

[adinapoli-iohk]

Good lad!