Consolidate the confirms under the same struct

[rach-id]

Currently, the ValsetConfirm and DataCommitmentConfirm structs are the same:

orchestrator-relayer/types/data_commitment_confirm.go

Lines 14 to 21 in 59db7a2

	type DataCommitmentConfirm struct {
	// Signature over the commitment, the range of blocks, the validator address
	// and the Ethereum address.
	Signature string
	// Hex `0x` encoded Ethereum public key that will be used by this validator on
	// Ethereum.
	EthAddress string
	}

orchestrator-relayer/types/valset_confirm.go

Lines 18 to 24 in 59db7a2

	type ValsetConfirm struct {
	// Ethereum address, associated to the orchestrator, used to sign the `ValSet`
	// message.
	EthAddress string
	// The `ValSet` message signature.
	Signature string
	}

We could look into consolidating them into the same struct.