Stage 1: post-processing validation and canton configuration

[carlpulley-da]

• unit testing for TotalInformeeValidator
• unit testing for TransactionNodesValidator
• unit testing for TransactionRootsValidator
• extend unit testing of ValueValidator, SignatoryValidator, StakeholderValidator and KeyMaintainersValidator to test against input contracts
• ensure all transaction tree validators can fail on submission in EngineTest
• ensure all transaction tree validators succeed on validation in EngineTest