Moves shared code into a mixin

What does this MR do?

Backport of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9073

Moves the shared code between CE and EE graphs components into a mixin Updates the CSS to reflect the EE changes

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/8688

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [-] Documentation created/updated via this MR
• [-] 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