Support X-Pack security

[munnerz]

Elasticsearch optionally supports security through X-Pack (when using a non-basic license).

Currently, it's hard coded to disabled x-pack auth in order to simplify the Pilot (as it's local elasticsearch client will need securely telling how to communicate with the ES API).

If the user has a valid non-basic license installed, we should allow the user to configure security/users/groups.

/kind feature /area elasticsearch

[munnerz]

As of Elasticsearch 6.x, x-pack security now requires TLS is configured on all nodes in order to use.

In order to manage this, it'd be ideal if we could utilise cert-manager in some form (to save duplicating CA management efforts).

[wallrj]

Part of: https://github.com/jetstack/navigator/issues/362