Track highlighter and dependency linker usage

What does this MR do and why?

To help us decide whether what we can do to dependency linking part of Gitlab::Highlight class, we track usage of Gitlab::Highlight and Gitlab::DependencyLinker.

This can help us get the following metrics:

• total usage of Gitlab::Highlight
• usage of dependency linker on blobs
• usage of dependency linker on diffs

How to set up and validate locally

1. Create a MR (MR A) with files that don't need dependency linking.
2. Create a MR (MR B) with a file that needs dependency linking (e.g. Gemfile).
3. View MR A. gitlab_highlight_usage metric should see an increase but dependency_linker_usage metric shouldn't increase.
4. View MR B. gitlab_highlight_usage metric should see an increase and dependency_linker_usage metric increases as well.

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.

Related to #435427 (closed)