Stream audit event CSV file

What does this MR do?

Stream audit event CSV file.

Before this MR

• Fetch in batch of 1k
• Write to a temp file on the server
• Once reached the limit 15Mb or completed writing the complete CSV, load the file in memory
• Dispatch it the client
• User will see a download box

In other words, we currently don't offer a streaming experience as intended. This is a current limitation with our CSV builder that affects all CSV downloads.

After this MR

• Fetch in batch of 1k
• Write to a stream
• Dispatch it the client
• User will see a download box

This feature is still under a feature flag audit_log_export_csv.

Screenshots

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

Availability and Testing

• 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

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team

Related to #246742 (closed)