Add new question feature

[weiquu]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• Feature addition or enhancement
• Code maintenance
• DevOps
• Improve developer experience
• Others, please explain:

Overview of changes:
Add a new question type, the multiple blanks question type. The syntax is very similar to other question types. An example is provided below:

<question type="multiBlanks" header="This question _______ is a '_______ blanks' question.">
  <q-option keyword="type"></q-option>
  <q-option keyword="multiple" reason="That's the name of the question type."></q-option>
</question>

The result will look like this:

Anything you'd like to highlight/discuss:
Still some things to be added, such as support for multiple keywords, setting a threshold, and making blanks inline with the question.

Testing instructions:

Proposed commit message: (wrap lines at 72 characters)
Add new question type for questions with multiple blanks

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Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No unrelated changes