Calculating migration cost of the wallet that cannot be migrated should return 403

[piotr-iohk]

Release	Operating System	Cause
next	Windows & OSX & Linux)	Code v Configuration v Environment v Human v Unknown

Context

#989 (comment)

We are returning 403 and error message when trying to migrate the wallets that are empty or contain only dust, however when calculating migration cost for such wallets we return 200 and migration cost = 0. This is somewhat inconsistent. We should be returning 403 and error message when calculating such migration cost too.

Note: for instance for estimating cost of transaction that is impossible to make due to insufficient funds, we return 403 -> https://github.com/input-output-hk/cardano-wallet/blob/master/lib/core-integration/src/Test/Integration/Scenario/API/Transactions.hs#L930-L951

Steps to Reproduce

1. Run BYRON_CALCULATE_02 integration test -> https://github.com/input-output-hk/cardano-wallet/blob/master/lib/core-integration/src/Test/Integration/Scenario/API/ByronWallets.hs#L154-L163

Expected behavior

We should return 403 and message (perhaps the same as when migrating such wallet):

I can't migrate the wallet with the given id: <wid>, because it's either empty or full of small coins which wouldn't be worth migrating.

Actual behavior

Currently it passes, asserts for 0 calculated cost.

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Resolution Plan

PR

Number	Base
#1008	master

QA

BYRON_CALCULATE_02 integration tests.

[piotr-iohk]

lgtm.