Add limit to snippet content size

What does this MR do?

This MR adds a limit to the snippet content size. This limit is set in the ApplicationSetting, although there isn't a UI page to set it. To change the limit the user will have to use the Rails console or the API.

The default limit is set to 50MB.

Refs #31133 (closed)

Screenshots

The error would look like:

The copy will adapt to the limit and current content size. If the limit is 50 MB, the copy would end ... The maximum size is 2 MB. The same goes for the current content size.

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