Content for customization schema

[casabre]

#19 requests a schema which can be applied to a customization file from any user. What should go into that schema. I want to start first with the schema extracted out of the example

{
    "stage": {
        "name": "any stage name",
        "tag": "can we reset a tag?",
        "label": "label setting should be possible",
        "replace": {
            "default key": "new value",
        },
    }
}

Any opinions @lambiase @glynos @sonshekar?