Handle error states for security reports

What does this MR do and why?

Prior to this MR, an error in any of the security reports API call would cause the widget to display a generic error. With this error, these errors are gracefully handled and now display an error for the scanner.

Screenshots or screen recordings

How to set up and validate locally

1. You'll need an EE License
2. You'll need to have runners enabled (See $2408961 for setting up a runner)
3. Enable :refactor_security_extension to turn this feature on.

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

1. Import https://gitlab.com/gitlab-examples/security/security-reports
2. Create a new MR by editing a file
3. Go to the MR page and check the widget

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 #382856 (closed)