PLT-3647 Email Batching (#3718)

* PLT-3647 Added config settings for email batching

* PLT-3647 Refactored generation of email notification

* PLT-3647 Added serverside code for email batching

* PLT-3647 Updated settings UI to enable email batching

* PLT-3647 Removed debug code

* PLT-3647 Fixed 0-padding of minutes in batched notification

* PLT-3647 Updated clientside UI for when email batching is disabled

* Go fmt

* PLT-3647 Changed email batching to be disabled by default

* Updated batched email message

* Added email batching toggle to system console

* Changed Email Notifications > Immediate setting to a 30 second batch interval

* Go fmt

* Fixed link to Mattermost icon in batched email notification

* Updated users to use 30 second email batching by default

* Fully disabled email batching when clustering is enabled

* Fixed email batching setting in the system console

* Fixed casing of 'Send Email notifications' -> 'Send email notifications'

* Updating UI Improvements for email batching (#3736)

* Updated text for notification settings and SiteURL.

* Prevented enabling email batching when SiteURL isn't set in the system console

* Re-added a couple debug messages

* Added warning text when clustering is enabled

utils/html.go

@@ -18,7 +18,7 @@ var htmlTemplates *template.Template
 
 type HTMLTemplate struct {
 	TemplateName string
-	Props        map[string]string
+	Props        map[string]interface{}
 	Html         map[string]template.HTML
 	Locale       string
 }
@@ -71,7 +71,7 @@ func InitHTMLWithDir(dir string) {
 func NewHTMLTemplate(templateName string, locale string) *HTMLTemplate {
 	return &HTMLTemplate{
 		TemplateName: templateName,
-		Props:        make(map[string]string),
+		Props:        make(map[string]interface{}),
 		Html:         make(map[string]template.HTML),
 		Locale:       locale,
 	}