Use v2 candidate receipts in parachain subsystems

[axaysagathiya]

Issue summary

use v2 of candidate receipt in parachain subsystems: Availability subsystem, Candidate validation subsystem, Candidate backing subsystem

Implementation details

add CandidateReceiptV2 and CommittedCandidateReceiptV2 types and use these types

type CandidateReceiptV2 struct {
	// The descriptor of the candidate.
	Descriptor CandidateDescriptorV2 
	// The hash of the encoded commitments made as a result of candidate execution.
	CommitmentsHash common.Hash
}

type CommittedCandidateReceiptV2 struct {
	// The candidate descriptor.
	Descriptor CandidateDescriptorV2
	// The commitments made by the parachain.
	Commitments CandidateCommitments
}

CandidateDescriptorV2 is already present.

As we want to update the code to use V2 of CandidateDescriptor, CandidateReceipt, and CommittedCandidateReceipt, many unit tests will be modified.

Acceptance criteria

• Make sure all unit tests pass