Option to return `refreshKeyValue` when not in devMode or using Cube Playground

**Is your feature request related to a problem? Please describe.**
The `refresh_key` value would be helpful for us to use on our frontend to display as a data freshness metric. It's available when running Cube locally but is removed in production:

```
const resObj = {
query: normalizedQuery,
lastRefreshTime: response.lastRefreshTime?.toISOString(),
...(
getEnv('devMode') ||
context.signedWithPlaygroundAuthSecret
? {
refreshKeyValues: response.refreshKeyValues,
usedPreAggregations: response.usedPreAggregations,
transformedQuery: sqlQuery.canUseTransformedQuery,
requestId: context.requestId,
}
: null
),
```

**Describe the solution you'd like**
Would it be possible to add a context variable that optionally allows key-value pairs from the conditionally included object to be returned in production?

**Describe alternatives you've considered**
This data can be retrieved via further queries from the frontend, but if many Cubes are being used to fetch data for a page, it introduces a lot more queries which are unnecessary when the data has already been retrieved but is being removed from the response.