[EE] Rename changelog files to have their less than 100 characters long

What does this MR do?

This is basically the EE port of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/31752.

We forgot to do that and it ended up causing mess down the road for the 12.2.2-rc31 (omnibus-gitlab#4629 (closed)). This was quick-fixed by omnibus-gitlab!3531 (merged) in the meantime.

Given that we are the 21st, the changelog will be compiled soon, and these files will be removed anyway, so we may not even need to merge this MR...

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team