Responder can respond to a push request

[hannahhoward]

Longer:
As a responder, I can respond a received push request, so that the requestor can determine if request was accepted

In:

• DataTransferModule's Receiver.ReceiveRequest should:
  • Validate the push request
  • If request validates, encode and send accepted response to requestor
  • If request doesn't validate, encode and send rejected response to requestor

Out:

• doing anything with the response

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Acceptance Criteria:

• Send push request over libp2p to another node
• Validate and respond on other side
• If request validates, should receive accepted response on other side
• If request doesn't validate, should receive rejected response on other side
• Referenced tests pass