Refactor mirror instructions view

What does this MR do?

In https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10779 we need to show a different message for LFS files sync.

In this MR we refactor a little bit the code to allow that small change.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Style guides
• Separation of EE specific content