Create snippet repository content

What does this MR do?

When a new snippet is created, we have to commit the file to the repository. For the MVP, we will only support one file (even though it will be stored in the repository).

At the moment, in the snippet model, the file name is optional, nevertheless, when it is committed to the repository we have to assign it a name. We are going to assign a custom name with the pattern snippetfileX.txt.

When we set the custom name, we have to check first whether there are any files with this name pattern. If there are, we have to retrieve which was the last index used and use it to generate the next custom name.

Refs #39265 (closed) and #199221 (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