This [replaces][1] the Split Security Reports app with the Security
Dashboard in the pipelines view. This is part of a larger effort to
[move security reports logic to the backend][2].

This is behind the `pipeline_report_api` feature flag, which is
currently disabled by default.

A few other related changes were made:

- Old references to "timeline" were replaced with "history" in specs
- DRY in some specs regarding state initialisation
- Make the history and count endpoint props optional on the dashboard
  component, which, if missing/empty, disable the display of the counts
  and charts components
- Fixes a rendering discrepancy in the vulnerability modal, which was
  displaying a `File: undefined` row

[1]: https://gitlab.com/gitlab-org/gitlab-ee/issues/13496
[2]: https://gitlab.com/groups/gitlab-org/-/epics/1425