Update MinimalPermissionsGuidancePlugin snippets

[garrytrinder]

{
    "$schema": "https://raw.githubusercontent.com/microsoft/dev-proxy/main/schemas/v0.18.0/rc.schema.json",
    "plugins": [
        {
            "name": "MinimalPermissionsGuidancePlugin",
            "enabled": true,
            "pluginPath": "~appFolder/plugins/dev-proxy-plugins.dll",
            "configSection": "minimalPermissionsGuidancePlugin"
        }
    ],
    "minimalPermissionsGuidancePlugin": {
        "filePath": "permissions-summary.json"
    }
}

configSection is no longer needed as we recommend that you should now use a reporter to obtain the output in a file, which means the config snippet can be removed as it won't be needed.