Update free CI minutes from 2000 to 400

What does this MR do?

In the GitLab.com settings page, the documentation mentions 2000 free CI minutes, yet this should be 400. The purpose of this MR is to fix that.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content