Bump sprig to v3.1.0 and mergo 3.11 (#1456)

* Bump sprig to v3.1.0
test for mergeOverwrite

* Let mergo not (accidentally) try to merge unexported fields

This is also a good chance separate `HelmState` with the config loaded from YAML, which I had been wanting to do for a long time.

Co-authored-by: Johannes Alkjær <johannes.alkjaer@wunderman.com>
Co-authored-by: Yusuke Kuoka <ykuoka@gmail.com>

pkg/tmpl/sprig_functions_test.go

@@ -0,0 +1,23 @@
+package tmpl
+
+import (
+	"testing"
+)
+
+func TestMergeOverwrite(t *testing.T) {
+	ctx := &Context{}
+	buf, err := ctx.RenderTemplateToBuffer(`
+		{{- $v1 := dict "bool" true  "int" 2 "str" "v1" "str2" "v1" -}}
+		{{- $v2 := dict "bool" false "int" 0 "str" "v2" "str2" "" -}}
+		{{- $mo1 := mergeOverwrite (dict) $v1 $v2 }}
+		{{- $mo1 -}}
+	`)
+	expected := "map[bool:false int:0 str:v2 str2:]"
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	actual := buf.String()
+	if actual != expected {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}