feat: Add dry_run support for reimport-scan operations

[Siryu6]

Description

This PR implements a dry_run feature for reimport-scan operations that allows users to preview what changes would occur during a reimport without making any database modifications.

Key Features:

• Optional dry_run boolean parameter (defaults to false) on reimport-scan API endpoints
• Returns detailed statistics about findings that would be created, reactivated, closed, or left untouched
• Respects all existing reimport parameters (close_old_findings, do_not_reactivate, severity filters, etc.)
• Non-breaking: all existing functionality remains unchanged

Use Case:
This feature is particularly useful for CI/CD pipelines where teams want to validate scan results and preview changes before merging to production environments.

API Response Example:

{
  "test_id": 123,
  "dry_run": true,
  "changes_preview": {
    "would_create": 5,
    "would_reactivate": 2,
    "would_close": 3,
    "would_leave_untouched": 10,
    "total_changes": 10
  },
  "findings_details": {
    "new_findings": [...],
    "reactivated_findings": [...],
    "closed_findings": [...],
    "unchanged_findings": [...]
  }
}

Documentation

API documentation is included in the serializer field descriptions (help_text).

Files Changed

• dojo/api_v2/serializers.py - API integration for dry_run parameter
• dojo/importers/default_reimporter.py - Core dry_run_reimport() logic
• dojo/importers/default_importer.py - Return signature update
• dojo/importers/options.py - dry_run parameter validation
• dojo/fixtures/dojo_testdata.json - Fixed missing SLA_Configuration
• dojo/engagement/views.py - View layer dry_run support
• dojo/test/views.py - View layer dry_run support
• unittests/dojo_test_case.py - Test helper methods
• unittests/test_import_reimport.py - Minor test adjustments
• unittests/test_import_reimport_dry_run.py - New comprehensive test suite

Labels to add:

• enhancement
• feature