Add API Fuzzing report type to backend

Problem

Backend doesn't support API Fuzzing reports. This prevents display of API Fuzzing results in the security dashboard.

Proposal

Add new report type to backend for API Fuzzing.

Report type: api_fuzzing Default filename: gl-api-fuzzing-report.json

Tasks:

1. Add new plan type column !43934 (merged)
2. Document new db field
3. Add new report type to backend
4. Update graphql schema
5. Add/update tests