Add test runs empty state to the the Project Quality Summary

What does this MR do and why?

For #344587 (closed)

This MR adds the empty state to be shown on the Project Quality Summary (Analytics -> CI/CD -> Project quality tab) when unit tests have not been set up to output results that we can display there.

This MR is behind the project_quality_summary_page feature flag, so it does not require a changelog or documentation (for now).

Screenshots or screen recordings

showing loading states	before	with this MR
no test runs data	Screen_Recording_2022-01-18_at_14.14.32	Screen_Recording_2022-02-15_at_17.42.28
with test runs data	Screen_Recording_2022-01-18_at_14.13.19	Screen_Recording_2022-02-15_at_17.43.34

How to set up and validate locally

1. have a GitLab Ultimate license loaded into your GDK
2. git checkout 344587-project-quality-no-test-runs-empty-state
3. echo "Feature.enable(:project_quality_summary_page)" | rails c
4. navigate to the Project Quality Summary page (Analytics -> CI/CD -> Project quality tab) for a project that does not have unit test reports set up
5. observe the empty state guiding you to set up unit test reports

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.