[Monitoring] New ES disable watch api not properly defined

[chrisronline]

Noticed in the obs edge cluster.

Could not set destination context: Invalid URL: https://34.203.1.122:9243_monitoring/migrate/alerts

The url format should start with a /.

Working: https://github.com/elastic/kibana/blob/master/x-pack/plugins/monitoring/server/kibana_monitoring/lib/monitoring_bulk.js#L44

New API: https://github.com/elastic/kibana/blob/master/x-pack/plugins/monitoring/server/es_client/monitoring_endpoint_disable_watches.ts#L16

[elasticmachine]

Pinging @elastic/stack-monitoring (Team:Monitoring)