Allow filtering of issues within boards by negate issue type in GraphQL

The GraphQL api is missing the ability to filter issues by negated issue type (i.e. not: { issue_type: "INCIDENT" }.

On the frontend, add support for this within issue boards.

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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.