MR Security widget performance improvements
This is a container for issues that will improve the performance of the MR security widget.
# 1. Limit number of entries in the MR widget
Instead of showing all the findings in the widget, this introduces a limit to the number of items that we display - and, by consequence, fetch from the backend.
The default limit is hard-coded but, if there is a scan result policy defined, we do our best to use that number instead. Findings, however, are always listed in decreasing severity order (i.e. critical first).
See [proposal in the design issue](https://gitlab.com/gitlab-org/gitlab/-/issues/339397/#proposal) for the new behavior requirements.
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# 2. Only load findings after "Expand"
Details in https://gitlab.com/gitlab-org/gitlab/-/issues/344467+
# 3. Poll pipeline status instead of individual reports - Complete
Details in https://gitlab.com/gitlab-org/gitlab/-/issues/371868+
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