Add scannedResourcesCsvPath to securityReportSummary

What does this MR do?

Merge requests that include a DAST scan, we want to allow the user to download a full list of URLs scanned by DAST in CSV format. The frontend will do this by providing a link to the appropriate CSV.

The MR creates the GraphQL endpoint the frontend will use to get the URL to the CSV file. However, since the CSV creation is not ready yet the endpoint will return NULL to allow the frontend to merge and deploy without breaking the MR page.

query{
  project(fullPath: "root/project"){
    pipeline(iid: "23"){
      securityReportSummary{
        dast{
++        scannedResourcesCsvPath
        }
      }
    }
  }
}

Relates to #223673 (closed)

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