Enable mTLS for Elastic Metrics

Currently the PeerAuthentications in logging only cover the elastic/kibana pods (see the podSelectors here). We will need to add an additional PeerAuthentication that restricts the the exporter to mTLS STRICT mode by default. Once this is in place we will also have to add the bits and pieces in Big Bang to modify the service monitor.

Acceptance Criteria:

• New PeerAuthentication in place with selector on the exporter pod
• ServiceMonitor configuration in Big Bang to handle usage of Istio's certs
• Metrics endpoint and all Elastic "services" healthy