Add ability to sort Dependency List by Severity

What does this MR do?

Adds ability to sort Dependency List by Severity.

This adds "Severity" to the available sorting options on the Dependency List. This will sort the dependencies according to the severity of any of their detected vulnerabilities.

This contributes towards the larger feature for adding dependency scanning results to the Dependency List, behind the dependency_list_vulnerabilities feature flag.

There is no backend support for this yet, though the UI portion still works if you enable the feature flag anyway; the returned list just won't be sorted as expected.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Style guides
• Separation of EE specific content

Performance 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