Split Severity and Confidence sets of values for Vulnerabilities

What does this MR do?

Splits the Severity and Confidence sets of values in line with the Back end.

Since this is the frontend component to a back end change, we should only merge this once the BE component is also completed.

Backend MR: !9495 (merged)

What are the relevant issue numbers?

#9397 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• EE specific content should be in the top level /ee folder
• Security reports checked/validated by reviewer