Datahub: Display search filter topic label in plural

[tkohr]

Description

This PR introduces proposes to change topic to topics in the search filter labels (just like formats). See https://camptocamp.atlassian.net/browse/GSHAUT-402. It might be worth discussing if we should display all search filter labels rather in plural or singular.

Also adds a small refinement on the geo badge.

Screenshot

Quality Assurance Checklist

• [ ] Commit history is devoid of any merge commits and readable to facilitate reviews
• [ ] If new logic ⚙️ is introduced: unit tests were added
• [ ] If new user stories 🤏 are introduced: E2E tests were added
• [ ] If new UI components 🕹️ are introduced: corresponding stories in Storybook were created
• [ ] If breaking changes 🪚 are introduced: add the breaking change label
• [ ] If bugs 🐞 are fixed: add the backport <release branch> label
• [ ] The documentation website 📚 has received the love it deserves

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This work is sponsored by geo2france.