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/user.go

@@ -2864,3 +2864,13 @@ func (a *App) UserIsFirstAdmin(user *model.User) bool {
 
 	return true
 }
+
+func (a *App) getAllSystemAdmins() ([]*model.User, *model.AppError) {
+	userOptions := &model.UserGetOptions{
+		Page:     0,
+		PerPage:  500,
+		Role:     model.SystemAdminRoleId,
+		Inactive: false,
+	}
+	return a.GetUsersFromProfiles(userOptions)
+}