Add related issues component to standalone vulnerability page

What does this MR do?

#9424 (closed) This MR adds a related issues block to the standalone vulnerabilities page, and lets the user link related issues to a vulnerability. It works the same way as the related issues block does on the Issues page, except that the ability to choose the relation type (relates to, blocks, blocked by) is disabled.

Demo

Peek_2020-07-07_01-13

How to test locally

https://gitlab.com/snippets/1956676

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