Adds option to create confidential issues

What does this MR do and why?

This adds an option to create confidential failure issues when running the relate-failure-issue command. This will unblock failure issue creation for CustomersDot as the failure details can't be public.

Related to gitlab-org/customers-gitlab-com#7563 (closed)

How to set up and validate locally

Run the following command

exe/relate-failure-issue --input-files "rspec-*.json" --project 48907354 --confidential --token "glpat-xxxxxxxxxxxxxxxxxxxx"

For the --input-files and --token options, download the rspec-e2e-mr.json json file and create an access token with api permission and Maintainer role in https://gitlab.com/gitlab-org/quality/customerdot-test-case-sessions-sandbox/-/settings/access_tokens.

⚠️ Note: Since this only works for newly created issues, you might need to delete some existing issues so that the script will create a new issue for it. Any existing issues that are not confidential will not be updated to confidential.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.