[Watcher] Disabling watcher in elasticsearch.yml doesn't disable watcher in kibana

[jgowdyelastic]

Kibana version: 7.3

Adding xpack.watcher.enabled: false to elasticsearch.yml doesn't disable watcher in kibana. Instead the plug in appears in a broken state.
It's possible to see the list of existing watches, but clicking on a watch hangs with a loading spinner.
Creating a watch lets you get to the end of the process before failing with a seemingly unrelated error.

[cjcenizal]

If Watcher is disabled on a node, it will only not run on that one node. So I think we can address this by hitting GET /_nodes and checking that settings.xpack.watcher.enabled is true on at least one of the nodes in the result:

{
  "nodes" : {
    "6r614rBHTCO-y-ahY-Ly3w" : {
      "settings" : {
        "xpack" : {
          "watcher" : {
            "enabled" : "false"
          }
        }
      }
    }
  }
}

[elasticmachine]

Pinging @elastic/es-ui (Team:Elasticsearch UI)