fix(custom resource state metrics): correctly convert status condition Unknown to a valid value

docs/metrics/extend/customresourcestate-metrics.md

@@ -337,7 +337,8 @@ Supported types are:
 * `nil` is generally mapped to `0.0` if NilIsZero is `true`, otherwise it will throw an error
 * for bool `true` is mapped to `1.0` and `false` is mapped to `0.0`
 * for string the following logic applies
-  * `"true"` and `"yes"` are mapped to `1.0` and `"false"` and `"no"` are mapped to `0.0` (all case-insensitive)
+  * `"true"` and `"yes"` are mapped to `1.0`, `"false"` and `"no"` are mapped to `0.0` (all case-insensitive)
+  * `"unknown"` is mapped to `-1.0` (all case-insensitive)
   * RFC3339 times are parsed to float timestamp  
   * Quantities like "250m" or "512Gi" are parsed to float using <https://github.com/kubernetes/apimachinery/blob/master/pkg/api/resource/quantity.go>
   * Percentages ending with a "%" are parsed to float

pkg/customresourcestate/registry_factory.go

@@ -131,9 +131,11 @@ type compiledCommon struct {
 func (c compiledCommon) Path() valuePath {
 	return c.path
 }
+
 func (c compiledCommon) LabelFromPath() map[string]valuePath {
 	return c.labelFromPath
 }
+
 func (c compiledCommon) Type() metric.Type {
 	return c.t
 }
@@ -477,6 +479,7 @@ func (e eachValue) DefaultLabels(defaults map[string]string) {
 		}
 	}
 }
+
 func (e eachValue) ToMetric() *metric.Metric {
 	var keys, values []string
 	for k := range e.Labels {
@@ -724,14 +727,17 @@ func toFloat64(value interface{}, nilIsZero bool) (float64, error) {
 		}
 		return 0, nil
 	case string:
-		// The string contains a boolean as a string
+		// The string is a boolean or `"unknown"` according to https://pkg.go.dev/k8s.io/apimachinery/pkg/apis/meta/v1#Condition
 		normalized := strings.ToLower(value.(string))
 		if normalized == "true" || normalized == "yes" {
 			return 1, nil
 		}
 		if normalized == "false" || normalized == "no" {
 			return 0, nil
 		}
+		if normalized == "unknown" {
+			return -1, nil
+		}
 		// The string contains a RFC3339 timestamp
 		if t, e := time.Parse(time.RFC3339, value.(string)); e == nil {
 			return float64(t.Unix()), nil