Clean up AppURL, remove legacy origin-url webcomponent (#37090)

1. `origin-url` was introduced in the past when there was no good
framework support to detect current host url
    * It is not needed anymore
    * Removing it makes the code clearer
2. Separate template helper functions for different templates (web
page/mail)
3. The "AppURL" info is removed from admin config page: it doesn't
really help.
    * We already have various app url checks at many places

modules/templates/page.go

@@ -24,13 +24,13 @@ type pageRenderer struct {
 }
 
 func (r *pageRenderer) funcMap(ctx context.Context) template.FuncMap {
-	pageFuncMap := NewFuncMap()
+	pageFuncMap := newFuncMapWebPage()
 	pageFuncMap["ctx"] = func() any { return ctx }
 	return pageFuncMap
 }
 
 func (r *pageRenderer) funcMapDummy() template.FuncMap {
-	dummyFuncMap := NewFuncMap()
+	dummyFuncMap := newFuncMapWebPage()
 	dummyFuncMap["ctx"] = func() any { return nil } // for template compilation only, no context available
 	return dummyFuncMap
 }