Add function to check if `config.Value` is valid (#1009)

## Changes

Small function broken out from other work in progress.

libs/config/value.go

@@ -51,6 +51,10 @@ func (v Value) Location() Location {
 	return v.l
 }
 
+func (v Value) IsValid() bool {
+	return v.k != KindInvalid
+}
+
 func (v Value) AsAny() any {
 	switch v.k {
 	case KindInvalid:

libs/config/value_test.go

@@ -35,3 +35,10 @@ func TestValueAsMap(t *testing.T) {
 	assert.True(t, ok)
 	assert.Len(t, m, 1)
 }
+
+func TestValueIsValid(t *testing.T) {
+	var zeroValue config.Value
+	assert.False(t, zeroValue.IsValid())
+	var intValue = config.NewValue(1, config.Location{})
+	assert.True(t, intValue.IsValid())
+}