Feature Request: gh projects item-list should support filtering by custom fields

[MarcPow]

Scenario: gh should enable filtering of items based on project metadata, either in the mainline CLI (gh issue) or in the gh extension (gh projects item-list).

[mntlty]

@MarcPow you can do this with the JSON output and jq or some other tool that speaks JSON. As an example:

gh projects item-list --org <YOUR_ORG> <PROJECT_NUMBER> --format=json | jq '.items[] | select(.status=="In Progress"  and .content.type == "Issue")’