Add ErrorReceipt to 04-channel protobuf definitions

[damiannolan]

Summary

ErrorReceipt defines a type which encapsulates the upgrade sequence and error associated with the
upgrade handshake failure. When a channel upgrade handshake is aborted both chains are expected to increment to the
next sequence.

message ErrorReceipt {
    uint64 sequence = 1;
    string error_msg = 2;
}

• sequence: Sequence contains the sequence at which the error occurred. Both chains are expected to increment to the next sequence after the upgrade is aborted.
• error_msg: ErrorMsg contains an arbitrary string which chains may use to provide additional information as to why the upgrade was aborted.

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[damiannolan]

#1613