fix: add nano contracts enabled

[andreabadesso]

Motivation

• The fullnode API now returns a nano_contracts_enabled field that indicates whether nano contracts are enabled on the network. The wallet-service needs to expose this information through its version endpoint.

Acceptance Criteria

• Version API returns nanoContractsEnabled field
• Field is validated as required boolean when receiving data from fullnode
• Field defaults to false when missing from older fullnode versions
• Database storage and retrieval of the field works correctly

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged
• Make sure either the unit tests and/or the QA tests are capable of testing the new features
• Make sure you do not include new dependencies in the project unless strictly necessary and do not include dev-dependencies as production ones. More dependencies increase the possibility of one of them being hijacked and affecting us.