Enable project ndjson ff by default

What does this MR do?

• Enables :project_import_ndjson feature flag by default
• Enables :project_export_as_ndjson feature flag by default

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

It was already tested and measured on staging #215007 (closed), #215004 (closed)

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Closes #216959 (closed)