feat(cli): send error notifications and snapshot reports (#4233)

* feat(cli): send error notifications and snapshot reports

Notifications will be sent to all configured notification profiles
according to their severity levels.

The following events will trigger notifications:

- Snapshot is created (CLI only, severity >= report)
- Server Maintenance error occurs (CLI, server and UI, severity >= error)
- Any other CLI error occurs (CLI only, severity >= error).

A flag `--no-error-notifications` can be used to disable error notifications.

* added template tests

* improved time formatting in templates

* plumb through notifytemplate.Options

* more testing for formatting options

* fixed default date format to RFC1123

cli/command_server_start.go

@@ -161,6 +161,9 @@ func (c *commandServerStart) serverStartOptions(ctx context.Context) (*server.Op
 		DebugScheduler:         c.debugScheduler,
 		MinMaintenanceInterval: c.minMaintenanceInterval,
 		DisableCSRFTokenChecks: c.disableCSRFTokenChecks,
+
+		EnableErrorNotifications: c.svc.enableErrorNotifications(),
+		NotifyTemplateOptions:    c.svc.notificationTemplateOptions(),
 	}, nil
 }