Support blank space naming for filter dropdown

Currently adding spaces in the names of filter options is not possible. The solution thus far has been to add dashes - where spaces would exist. But this impairs readability and scanability of the filters list 🙁

Considerations

1. Using spaces today in the filter bar breaks the query (example video)
2. Make sure that old URLs, using the current - format still work.

Relevant Files

The Magic 🎩

• https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/filtered_search/filtered_search_dropdown_manager.js#L160
• https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/filtered_search/filtered_search_token_keys.js#L52
• https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/filtered_search/filtered_search_manager.js#L734

CE Labels using dashes

• "my-reaction" > https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/filtered_search/available_dropdown_mappings.js#L104
• "target-branch" > https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/filtered_search/available_dropdown_mappings.js#L138

EE Labels using dashes

• "approved-by" > (not yet merged) !30335 (merged)