Add modals and actions for the vulnerabilities in the Group security dashboard

What does this MR do?

Note: The information icon is black because the fill color is baked in to the SVG in the SVG repo. I've created an MR to remedy that. gitlab-svgs!157 (merged)

What are the relevant issue numbers?

#6709 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [?] Documentation created/updated
• Tests added for this feature/bug
• 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
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?