chore(GlTooltip): contain examples

What does this MR do?

To be properly displayed in design.gitlab.com, tooltips need to be contained to their own container to prevent them from being appended to the body where GitLab UI styles won't be applied.

Re gitlab-org/gitlab-services/design.gitlab.com!2165 (comment 447180036)

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: mr_url
  • CustomersDot: mr_url
  • Status Page: mr_url
• Added the ~"component:*" label(s) if applicable.