Add Carousel Styles to GitLab UI

What does this MR do?

This MR adds basic Styling to the GL-Carousel component. These styles are being moved from the GitLab Project, since they are quite generic they are better off living in GitLab UI.

The progress on this is tracked in this Issue: gitlab#297540 (closed)

Note: since the Carousel is currently only used in the GitLab Repo, only one according MR is needed.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.
• [-] If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• [-] If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
• If the MR changes a component's API, integration MR(s) have been opened in the following projects to ensure that the @gitlab/ui package can be upgraded quickly after the changes are released:
  • GitLab: gitlab!51704 (diffs)
  • CustomersDot: mr_url
  • Status Page: mr_url
• Added the ~"component:*" label(s) if applicable.

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] Security reports checked/validated by a reviewer from the AppSec team