IMPORTANT: All PRs must be linked to an issue (except for extremely trivial and straightforward changes).

Fixes #2505

Description
In the DropDownViewHolderFactory the hyphen("-") is being set as the default answer option to the drop down. Instead of setting it a fixed answer I have made it configurable. To change the default answer option the questionnaire item representing the drop down item will have the initial property which will have a valueString. The default answer option will be filled with the initial property value if available else it will be filled hyphen("-").
This approach ensures that the configuration will be done via questionnaire itself and the code need be changed everytime to change a default answer option.

Alternative(s) considered
Have you considered any alternatives? And if so, why have you chosen the approach in this PR?

Type
Bug Fix.

Screenshots (if applicable)

Checklist

• I have read and acknowledged the Code of conduct.
• I have read the Contributing page.
• I have signed the Google Individual CLA, or I am covered by my company's Corporate CLA.
• I have discussed my proposed solution with code owners in the linked issue(s) and we have agreed upon the general approach.
• I have run ./gradlew spotlessApply and ./gradlew spotlessCheck to check my code follows the style guide of this project.
• I have run ./gradlew check and ./gradlew connectedCheck to test my changes locally.
• I have built and run the demo app(s) to verify my change fixes the issue and/or does not break the demo app(s).