Add counting logic to snippet statistics

What does this MR do?

In this MR we add the necessary logic to track and store the fields we want from the repository, which are:

• file count
• commit count
• repository size

Refs #223700 (closed)

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