Create a new component specifically for updating severity

Create a new component that includes GlModal, designed to be a generic solution for use whenever a user can override the severity. here is an example from the design.

1. Create and use GraphQL query to fetch all severities, similar to:

   #import "ee/security_dashboard/graphql/fragments/vulnerability_severities_count.fragment.graphql"
   
   query GetVulnerabilitySeverities { vulnerabilities { ...VulnerabilitySeveritiesCount } }

2. Create a GraphQL mutation query for updating the user's selection.