Fix evaluation with latest cue 0.3.2 release

Since cue beta.8, cue takes forever to evaluate envs-ng.

Odly it is due to this part in the loki config

-			if strings.HasSuffix(_lokiFlavorMap[_lokiFlavor].retention, "d") {
-				retention_string_days:  strings.TrimSuffix(_lokiFlavorMap[_lokiFlavor].retention, "d")
-				retention_int:          strconv.ParseInt(retention_string_days, 10, 0) * 24
-				retention_string_hours: strconv.FormatInt(retention_int, 10) + "h"
-				values: loki: index: retention_period: retention_string_hours

Doing the conversion in a let seems to workaround the issue.

Also, fixed the _lokiFlavorMap to only generate values for the given _lokiFlavor.