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

api/admin.go

@@ -156,6 +156,10 @@ func reloadConfig(c *Context, w http.ResponseWriter, r *http.Request) {
 	}
 
 	utils.LoadConfig(utils.CfgFileName)
+
+	// start/restart email batching job if necessary
+	InitEmailBatching()
+
 	w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
 	ReturnStatusOK(w)
 }
@@ -204,6 +208,9 @@ func saveConfig(c *Context, w http.ResponseWriter, r *http.Request) {
 	// 	}
 	// }
 
+	// start/restart email batching job if necessary
+	InitEmailBatching()
+
 	rdata := map[string]string{}
 	rdata["status"] = "OK"
 	w.Write([]byte(model.MapToJson(rdata)))