Handle non-ASCII characters for topic_explore_projects_path
What does this MR do and why?
See https://gitlab.com/gitlab-org/gitlab/-/issues/393166 first
- Fix explore topic path to render non ASCII characters
- Do not allow certain characters for Projects::Topic#topic_name
- Follow-up !122970 (comment 1422903154)
Related issue: https://gitlab.com/gitlab-org/gitlab/-/issues/393166
Screenshots or screen recordings
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How to set up and validate locally
See https://gitlab.com/gitlab-org/gitlab/-/issues/393166
MR acceptance checklist
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I have evaluated the MR acceptance checklist for this MR. 
Edited  by Thong Kuah