Extend empty state component to support description links

Currently, many of the empty states are using description links within the empty state description (e.g. More information) (see helping users). For example, see https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/7967. However, the empty-state component doesn't support inserting links in the description.

The following example in feature flags empty state section, which utilizes the empty-state component from gitlab-ui should use a link instead of primary CTA button. See https://gitlab.com/gitlab-org/gitlab-ee/issues/9230.

Possible	Not possible