Add graphQL mutation for destroying issue boards

What does this MR do?

It adds a graphql mutation for removing issue boards.

Example

mutation {
  destroyBoard(input: {id: "gid://gitlab/Board/2"}) {
    errors
  }
}

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

Issue: #233455 (closed)