Resolve "Extend utility classes for `gitlab-ui`search-box"

What does this MR do?

Adds the following utility class:

• pointer: Adds a cursor: pointer

Adds a spacer to our variables_overrides to leverage pl-6 and pr-6:

$spacers: (
  6: ($spacer * 8)
);

These utility classes are required by gitlab-ui!181 (merged)

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/58202

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer

Closes #58202 (closed)