Remove `unwrap` & Add clippy lint option to check the use of `unwrap`

[dayeon5470]

Background

• The development rules for our product say that we should use expect instead of unwrap in situations where we are confident that panic will not necessarily occur.
• We should also make sure that the code we write in the future follows the same rules.
• Therefore, we should proceed with the modification as shown below

Task

• Remove unwrap(), which is used against the rules
• Add a lint option to the Clippy part of ci.yml: -W clippy::unwrap_used

[sophie-cluml]

@dayeon5470 We should not mention private links.