Coin Selection GraphQL API

[Voxelot]

The SDK should use a special API to select which utxos to use as inputs, instead of directly picking utxos from the full set. This is important for ensuring consistent behavior across SDK's and the ability to implement efficient dust mitigation strategies such as random-improve.

For inputs, the API will take:

owner: The Address of the utxo owner
spend_query: Vec<(AssetId, Amount)> The total amount of each asset type to spend
max_inputs: u8 The max number of utxos that can be used

Success:
Return a list of utxos <= max_inputs that will satisfy the amounts to be spent.

Errors:

• If the spend amount is higher than the available balance of the owner.
• If reaching the spend amount requires the list of utxos to be greater than max_inputs

[Voxelot]

@digorithm this is done, and will be available in the next release. Integration testing could start using the published docker image from master branch.