Rebuild channel index (#26080)

* WIP

* Added rebuild channels index functionality

* Added rough logic to send message to all sysadmins

* WIP

* WIP

* WIP

* Cleanup

* i18n fix

* reading through all pages of system admins

* Fixed webapp style

* i18n fix

* Added help text

* i18n fix

* i18n update

* Updated system console button action

* Updated snapshots

* some cleanup

* Updated snapshot

* Update server/channels/app/server.go

Co-authored-by: Daniel Espino García <larkox@gmail.com>

* fixed typo

* Refactoring to improve readibility

* moved index check to API later during config update

* Added some docs

* Updated get system bot

---------

Co-authored-by: Daniel Espino García <larkox@gmail.com>

server/channels/app/config.go

@@ -64,6 +64,10 @@ func (a *App) AddConfigListener(listener func(*model.Config, *model.Config)) str
 	return a.Srv().platform.AddConfigListener(listener)
 }
 
+func (a *App) AddLicenseListener(listener func(oldLicense, newLicense *model.License)) string {
+	return a.Srv().platform.AddLicenseListener(listener)
+}
+
 // Removes a listener function by the unique ID returned when AddConfigListener was called
 func (a *App) RemoveConfigListener(id string) {
 	a.Srv().platform.RemoveConfigListener(id)