Frontmatter description doesn't render unless there are tabs

Currently, we are rendering description: at the top of the page, but only if the pages contains tabs. This description should always render, regardless of whether there are tabs or not. A lot of pages don't contain tabs, so we'll never be able to utilize the description: unless there is a vueComponent associated with that component.

For example, we are creating an overview page that utilizes the description: item: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/issues/1105. We are also updating the docs pages to utilize a new doc template, which utilizes the description: item, so if the components without a Vue component get updated to the new template, those updates will be blocked until this is resolved.