ExtractQueryLimitsContext gets the embedded limits from the context.

ExtractQueryLimitsHTTP retrieves the query limit policy from the HTTP header and returns it.

InjectQueryLimitsContext returns a derived context containing the provided query limits.

InjectQueryLimitsHeader adds the query limits to the headers.

InjectQueryLimitsHTTP adds the query limits to the request headers.

NewQueryLimitsMiddleware creates a middleware that extracts the query limits policy from the HTTP header and injects it into the context of the request.

NOTE: we use custom `model.Duration` instead of standard `time.Duration` because, to support user-friendly duration format (e.g: "1h30m45s") in JSON value.