Disable telemetry in e2e tests

[pebrc]

We don't want to report telemetry data out of e2e test runs. Kibana has different settings depending on its version to achieve that:

• 6.8-7.5: xpack.xpack_main.telemetry.enabled
• > 7.5: telemetry.enabled

When set to false Kibana stops reporting telemetry data and on newer version also stops serving the internal telemetry/v2/clusters/_stats route (tbd since which version)

The problem with disabling telemetry on older versions is that Kibana makes an optimise run which which leads to OOM as we don't run Kibana with enough resources to successfully complete the run.

A few options come to mind:

• give Kibana enough resources to complete the optimisation (might be a lot and limit the ability to run the full e2e suite on resource constrained environments like kind)
• disable optimise in configuration with optimize.enabled=false (might hide real world resource starvation problems, but arguably e2e test are not good environment to verify default memory settings )
• use a different approach external to Kibana like a k8s NetworkPolicy preventing egress from the Kibana pod (only recent versions of Kibana with make requests from the server anyway, tbd since which version)

[barkbay]

I'm wondering if we could add an host alias to the podTemplate to force the telemetry server to be resolved as localhost :

  hostAliases:
  - ip: "127.0.0.1"
    hostnames:
    - "telemetry.elastic.co"

[david-kow]

Another option worth investigating is to try enabling sending telemetry data to staging cluster for E2E tests: https://github.com/elastic/kibana/blob/master/src/plugins/usage_collection/README.md#testing.