Ability to bypass traffic filters for watcher http input

[jguay]

Description

Watcher currently allow to bypass traffic filters in Elasticsearch Services for webhook action only by settings xpack.notification.webhook.additional_token_enabled

There is no such possibility for watcher http input so no way to query a remote elasticsearch cluster with http input when using traffic filters

The workaround solution is to set up cross-cluster search which is compatible with traffic filtering

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)