[feat] Support fill-in-the-blank questions in the exam environment

[nieldakarla]

Currently, the exams do not support fill-in-the-blank questions for the languages exams. Only multiple choice are allowed.

This prevents us from including fill-in-the-blank questions that are already used in the curriculum and are pedagogically important, especially for assessing grammar, vocabulary, and form recognition.

Current behavior:

• Fill-in-the-blank questions cannot be added in the exam environment.

Expected behavior:

• The exam environment should support fill-in-the-blank questions.
• Learners should be able to type an answer into one or more blanks.

Answers should be validated against predefined correct responses (with support for exact matches and, if possible, acceptable variations).

Supporting fill-in-the-blank questions would allow better alignment between the learning content and the exam, and enable more accurate assessment of learner's skills.