On GraphQL boards, add support for milestone wildcard search

This is the frontend part of #337687 (closed)

Simply remove defaultMilestones from tokens in issue_board_filtered_search.vue and make sure the following shows up in search:

• None
• Any
• Upcoming
• Started

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Feature Flag

We're working on refactoring filtered search on boards to use GraphQL. This issue is part of that work, and is behind the :issue_boards_filtered_search feature flag.