Add SAST scan API endpoint

Problem to solve

To perform security scans from the IDE in real-time, we intend to use a REST API endpoint.

The endpoint is available only to Ultimate customers, and although this change supports both SaaS and Self-managed instances, cloud connector doesn't currently support Ultimate only, non-addon Self-managed unit primitives.

Note: according to https://handbook.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#when-to-use-feature-flags, we are adding the endpoint without a feature flag.

Proposal

1. add an Ultimate only feature
2. add a project policy limits to developers, maintainers, and owners
3. add a new service and scope to cloud connector access_data.yml with no cut_off_data
4. add endpoint handler of POST /projects/:id/security/scan
   1. relay file path and content to CC backend
5. add tests
6. add documentation