Save Draft changes functionality creates multiple Questionnaire Responses instead of updating existing one

[Rkareko]

Describe the bug
MVP drafting feature was implemented on #3541 . One of the assumptions for that implementation is that there would only be one draft (QR with status in-progress) per form (Questionnaire) at a time.

The current implementation creates an new draft (QR with status in-progress) every time the user does a Save Draft.

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior
The same draft (QR with status in-progress) should be updated every time a Save Draft operation is performed.

Screenshots
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Smartphone (please complete the following information):

• Device: [e.g. Samsung Galaxy A2 emulator]
• Android version: [e.g. Settings -> About phone -> Android version]
• Build number: [e.g. Settings -> About phone -> Build number]
• Version [e.g. 24]

Additional context
Add any other context about the problem here.