feat(Button): Add badge in button examples
Problem
Badge-in-button examples aren't present in Pajamas.
Solution
- Add badge example from https://gitlab-org.gitlab.io/gitlab-ui/?path=/story/base-button--badges.
- Add badge with SR only text example from https://gitlab-org.gitlab.io/gitlab-ui/?path=/story/base-button--badge-with-sr-only-text.