Update features API endpoint to use GitHub API

[viktorix]

We need to modify JSON generator script to get data from GitHub, which is triggered periodically using a cronjob.

The following is a proposed JSON format based on the current API:

{
    "recent": {
        "data": [{
                "title": "items->{}->title",
                "status": "open",
                "link": "items->{}->url"
            },
            {
                "title": "items->{}->title",
                "status": "open",
                "link": "items->{}->url"
            }
        ]
    },
    "in-progress": {
        "data": [{
                "title": "items->{}->title",
                "status": "needs-pr",
                "link": "items->{}->url"
            },
            {
                "title": "items->{}->title",
                "status": "has-pr",
                "link": "items->{}->url"
            }
        ]
    },
    "help-wanted": {
        "data": [{
                "title": "items->{}->title",
                "status": "open",
                "link": "items->{}->url"
            },
            {
                "title": "items->{}->title",
                "status": "open",
                "link": "items->{}->url"
            }
        ]
    },
    "link": "https://github.com/ClassicPress/ClassicPress/issues?q=is%3Aopen+is%3Aissue+label%3A%22type%3A+feature+request%22"
}

Categorization

We have 3 categories: recent, in-progress, and help wanted

recent

Pull the most recent 10 open issues using the label "type: feature request" and the following statuses:

• status: discussion
• status: on hold
• status: need more info
• status: needs decision

When passing status label to the JSON file, please remove "status: ".

https://api.github.com/search/issues?q=is%3Aissue+is%3Aopen+label%3A%22type%3A+feature+request%22+repo:classicpress/classicpress

in progress

Pull open issues labeled "type: feature request" and the following statuses:

• status: has pr
• status: needs pr
• status: research plugin
• status: needs test
• status: needs review
• status: community reviewed

When passing status label to the JSON file, please remove "status: ".

https://api.github.com/search/issues?q=is%3Aissue+is%3Aopen+label%3A%22type%3A+feature+request%22+repo:classicpress/classicpress

help wanted

Pull the latest 10 open issues with label "help wanted".
When passing status label to the JSON file, please remove "status: ".

https://api.github.com/search/issues?q=is%3Aissue+is%3Aopen+label%3A%22help+wanted%22+repo:classicpress/classicpress