Display summary highlights

What does this MR do and why?

The MR Security Widget displays in a summary the total count of vulnerabilities split by severity in the summary. This commit adds that functionality.

Screenshots or screen recordings

With no new vulnerabilities	With new vulnerabilities

How to set up and validate locally

1. This feature is behind a feature flag. Enable :refactor_security_extension to turn this feature on.

echo "Feature.enable(:refactor_security_extension)" | rails c

1. Visit an MR page with Security Scanning

The easiest way to populate data for testing is using this extension https://chrome.google.com/webstore/detail/mokku-mock-api-calls-seam/llflfcikklhgamfmnjkgpdadpmdplmji?hl=en and importing mokku-mocks-17-8-2022.json this json.

Once you have enabled the extension:

1. Open the developer tools
2. Find Mokku tab
3. Click on import
4. Import the file mentioned above

Expected design

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.

Related to #365502 (closed)