Updating transcriptListPublisher to pass back previousTranscriptNextToken

[mliao95]

Issue Number:

Description:

What are the changes? Why are we making them?

This PR updates the transcriptListPublisher logic.

• Returns TranscriptData object which contains the original transcriptList property as well as a previousTranscriptNextToken string property.
  • previousTranscriptNextToken represents the nextToken that will fetch the next batch of older transcripts
• Adding debounce to transcriptListPublisher updates to reduce the number of handler calls. Original behavior would call the update event for each message in a getTranscript result (i.e. if getTranscript returned 100 messages, it would trigger 100 times).

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Functional backward compatibility:

Does this change introduce backwards incompatible changes? [YES/NO]

YES

Does this change introduce any new dependency? [YES/NO]

NO

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Testing:

Is the code unit tested?

YES

Have you tested the changes with a sample UI (e.g. Android Mobile Chat Example)?

List manual testing steps:

• Add Steps below:

Here are a list of manual test cases to run through:

• Initiating chat and connecting with an agent
• Retrieving transcript
• Disconnecting from chat
• Sending a message to the agent
  • See typing bubbles on agent side
  • See read/delivered receipt on client side
  • Receiving a message from the agent
  • See typing bubbles on client side
  • See read/delivered receipt on agent side
  • Sending an attachment to the agent (try .txt, .pdf, .jpg)
  • Preview the attachment on click
  • Receiving an attachment from the agent
  • Preview the attachment on click
• Close the application (Without ending chat) → open app again → Start chat → Should Retrieve transcript from a previous chat session