Create snippet repository model

What does this MR do?

In this MR we actually create the snippet repository model. This doesn't mean that git actions are allowed. This MR just introduces this class and refactors some existent code.

Refs #39176 (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