Set custom SLI for end points in Pipeline Insights

Problem to Solve

There are a few end points that have a target duration of 1s, and it has pushed the availability below the threshold:

1. Projects::MergeRequestsController#test_reports
2. Projects::Pipelines::TestsController#show
3. Projects::ArtifactsController#browse
4. Projects::ArtifactsController#file
5. Projects::Pipelines::TestsController#summary
6. GET /api/:version/projects/:id/jobs/artifacts/:ref_name/download
7. GET /api/:version/projects/:id/jobs/:job_id/artifacts/*artifact_path
8. Projects::PipelinesController#test_report
9. Projects::ArtifactsController#latest_succeeded

Proposal

Let's change these end points to low urgency at 5s.