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.go

@@ -12,3 +12,7 @@ func (a *Args) Arg(x any) string {
 	*a = append(*a, x)
 	return "?"
 }
+
+func (a *Args) GetArgs() Args {
+	return *a
+}