SMTP: Update email templates to include populated <title> tag (#61430)

* add .TemplateData property to data in order to populate template <title> tags with the compiled subject value

* update all templates

* re-enable integration test and update implementation to check changes

* chore: fmt

* add HiddenSubject template func and update text templates

* slight performance improvement, only execute subject template once

* update template I missed

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Co-authored-by: Gilles De Mey <gilles.de.mey@gmail.com>

pkg/services/notifications/email.go

@@ -33,4 +33,9 @@ func setDefaultTemplateData(cfg *setting.Cfg, data map[string]interface{}, u *us
 	if u != nil {
 		data["Name"] = u.NameOrFallback()
 	}
+	dataCopy := map[string]interface{}{}
+	for k, v := range data {
+		dataCopy[k] = v
+	}
+	data["TemplateData"] = dataCopy
 }