write_acknowledgement handler incorrectly uses packet's source_{port, channel} as key for storing acks

[hu55a1n1]

Summary of Bug

modules/src/core/ics04_channel/handler/write_acknowledgement::process incorrectly uses packet's source_{port, channel} instead of dest_{port, channel} as key for storing acks. See spec -> https://github.com/cosmos/ibc/tree/master/spec/core/ics-004-channel-and-packet-semantics#writing-acknowledgements

function writeAcknowledgement(
  packet: Packet,
  acknowledgement: bytes) {
    // ...
    
    // write the acknowledgement
    provableStore.set(
      packetAcknowledgementPath(packet.destPort, packet.destChannel, packet.sequence), // <--------- here
      hash(acknowledgement)
    )
    
    // ...

Version

v0.16.0

Acceptance Criteria

write_acknowledgement handler is fixed to use the appropriate port/channel ids.

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