Cache vulnerability history per project

This work is to address https://gitlab.com/gitlab-org/gitlab-ee/issues/11693

This is a short-term and likely temporary solution to address the timeouts we are seeing on the vulnerabilities history endpoint on the group security dashboard.

This is behind a group-based feature flag.

The approach taken is to cache the results for the vulnerabilities history endpoint per project. We can't cache at the group level because the data can be filtered and because every time a pipeline runs for a project in the group, the entire cache would be stale. Instead, we're caching the results per projects and then aggregating them for the history endpoint for the group security dashboard.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance 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