Inconsistent elasticsearch settings between modules and metrics/monitoring

*Original comment by @robbavey:*

The settings for elasticsearch properties for modules and metrics/configuration management is inconsistent, particularly with regard to how security is handled:

| Property | Module Key | Metric Key |
|----------------------------|---------------------------------------------|-------------------------------------------------------|
| Elasticsearch Hosts | var.elasticsearch.hosts | xpack.monitoring.elasticsearch.url |
| Certificate Authority | var.elasticsearch.ssl.certificate_authority | xpack.monitoring.elasticsearch.ssl.ca |
| Turn off host verification | var.elasticsearch.ssl.verification_mode | xpack.monitoring.elasticsearch.ssl.verification_mode |
| SSL Enabled | var.elasticsearch.ssl.enabled | NOT EXPLICITLY ENABLED |
| Path to certificate for client auth | var.elasticsearch.ssl.certificate | NO SETTING |
| Path to key for client auth| var.elasticsearch.ssl.key | NO SETTING |
| Path to Truststore | NO SETTING |xpack.monitoring.elasticsearch.ssl.truststore.path |
| Truststore Password | NO SETTING |xpack.monitoring.elasticsearch.ssl.truststore.password |
| Client certificate keystore| NO SETTING |xpack.monitoring.elasticsearch.ssl.keystore.path |
| Client certificate password| NO_SETTING |xpack.monitoring.elasticsearch.ssl.keystore.password |