Add severity badge to security reports

What does this MR do?

This MR adds the severity badge to the security reports on the MR request so that the user can more quickly see the severity of issues

It also unifies the way the severity label is displayed in the same way across all related components, so that they can be potentially consolidated with #207243 (closed)

Screenshots

Before

After

Note: Some of this data was mocked

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Relates to #34352 (closed)

Relates to #207243 (closed)

Relates to #199145 (closed)