Add None and Any filters for Author and Assignee in new filtered search for issue boards.

Setup

• rails c
• Feature.enable(:issue_boards_filtered_search)
• Go to a project or group issue boards

Issue

As pointed out https://gitlab.slack.com/archives/CETG54GQ0/p1639978896137100

We need to add the None option to the Assignee and Author dropdown.

We also need to update the URL params to be assignee_id or assignee_wildcard_id to support the wildcards None and Any for the filters.

Currently, the Any filter on Author and Assignee in Issue Boards filtered search with the FF on is not working correctly.