Update project topics styling to use badges design

Problem to solve

We're renaming project tags to project topics in https://gitlab.com/gitlab-org/gitlab-ce/issues/54167. We considered doing a styling update at the same time, but we're waiting on a dependency in https://gitlab.com/gitlab-org/csslab/issues/50 before we can proceed with the styling change.

Proposal

• Present topics on the project overview page with the same pattern we use for badges.
• Clicking the tag should link to filtering projects by the tag, /explore?tag=TAG_TO_FILTER_ON.

Links / references