Implement createCCU function for chain connector plugin

[ishantiw]

Description

Implement createCCU function which the following params,

• sendingChainId - Config property of the plugin
• Certificate - returned by getNextCertificateFromAggregateCommits
• activeValidatorsUpdate: from the getActiveValidatorsDiff Implementation
• newCertificateThreshold: If the certificateThreshold used to create certificate.validatorsHash is different from the one stored in the chain account, include the new value in the newCertificateThreshold property. By checking the certificateThreshold with the certificateThreshold received from getBFTParameters
• inboxUpdate: The property inboxUpdate.crossChainMessages lists all CCMs that have been included in the sidechain outbox up to h2 (and which have not been included on the sidechain yet).
  • In this case, the messageWitness will be empty. we can get CCMs from interoperability_getChannel and check the outbox of the receiving chain which is mainchain here.
  • Compute the inclusion proof for the outbox root of the sidechain account into the mainchain state root. This proof is then used to compute inboxUpdate.outboxRootWitness

Acceptance Criteria

• Should have all the unit tests relevant for the CCU creation

Additional Info

• It will be better to use all the validity conditions listed here in LIP0053#parameters-validity