Add Namespace filter to shared Vue components

Proposal

Add Namespace filter support to app/assets/javascripts/groups_projects/components/tabs_with_list.vue

Implementation guide

1. Create a new namespace_token.vue in app/assets/javascripts/vue_shared/components/filtered_search_bar/tokens
2. Use logic in app/assets/javascripts/vue_shared/components/filtered_search_bar/tokens/user_token.vue but call app/assets/javascripts/api.js#L233
3. Add a token definition to app/assets/javascripts/groups_projects/components/tabs_with_list.vue#L136 using the new namespace_token.vue component