Unified Storage: in SQL template, also handle output data, improve API, examples and docs (#87560)

* preview of work so far

* stylistic improvements

* fix linters

* remove golden tests, they may cause the system to be too rigid to changes

* remove unnecessary code for golden tests

* remove white space mangling in Execute

* also handle output data, improve API, examples and docs

* add helper methods

* fix interface

pkg/services/store/entity/sqlstash/sqltemplate/args_test.go

@@ -1,8 +1,6 @@
 package sqltemplate
 
-import (
-	"testing"
-)
+import "testing"
 
 func TestArgs_Arg(t *testing.T) {
 	t.Parallel()
@@ -22,7 +20,7 @@ func TestArgs_Arg(t *testing.T) {
 	shouldBeQuestionMark(t, a.Arg(3))
 	shouldBeQuestionMark(t, a.Arg(4))
 
-	for i, arg := range *a {
+	for i, arg := range a.GetArgs() {
 		v, ok := arg.(int)
 		if !ok {
 			t.Fatalf("unexpected value: %T(%v)", arg, arg)