ElasticSearch metrics configuration

Configuration of the export of metrics into ElasticSearch

Name	Environment	Description	Default value
`ontrack.extension.elastic.metrics.allow-drop`	`ONTRACK_EXTENSION_ELASTIC_METRICS_ALLOW_DROP`	Set to false to disable the deletion of the index when performing a re-indexation	true
`ontrack.extension.elastic.metrics.debug`	`ONTRACK_EXTENSION_ELASTIC_METRICS_DEBUG`	Must we trace the behaviour of the export of the metrics in the logs?	false
`ontrack.extension.elastic.metrics.enabled`	`ONTRACK_EXTENSION_ELASTIC_METRICS_ENABLED`	Is the export of metrics to Elastic enabled? Elasticsearch is used for nothing else: when disabled, the default, no Elasticsearch client is created and Spring Boot's Elasticsearch auto-configuration and health indicator are left out.	false
`ontrack.extension.elastic.metrics.index.immediate`	`ONTRACK_EXTENSION_ELASTIC_METRICS_INDEX_IMMEDIATE`	Flag to enable immediate re-indexation after items are added into the index (used mostly for testing. It should not be used in production. If set to true, this overrides the asynchronous processing of the metrics	false
`ontrack.extension.elastic.metrics.index.name`	`ONTRACK_EXTENSION_ELASTIC_METRICS_INDEX_NAME`	Name of the index to contains all Ontrack metrics	ontrack_metrics
`ontrack.extension.elastic.metrics.queue.buffer`	`ONTRACK_EXTENSION_ELASTIC_METRICS_QUEUE_BUFFER`	Bulk update capacity. When the number of metrics reaches this amount, the metrics are sent to Elastic.	512
`ontrack.extension.elastic.metrics.queue.capacity`	`ONTRACK_EXTENSION_ELASTIC_METRICS_QUEUE_CAPACITY`	Maximum capacity for the queue. If the queue exceeds this capacity, new events will be on hold.	1024
`ontrack.extension.elastic.metrics.queue.flushing`	`ONTRACK_EXTENSION_ELASTIC_METRICS_QUEUE_FLUSHING`	Every such interval, the current buffer of metrics is flushed to Elastic (expressed by default in minutes)	PT1M
`ontrack.extension.elastic.metrics.target`	`ONTRACK_EXTENSION_ELASTIC_METRICS_TARGET`	Defines where the Elastic metrics should be sent. Possible values are: * MAIN - When this option is selected, the ES instance defined by the `spring.elasticsearch.` properties will be used. CUSTOM -When this option is selected, the ES instance defined by the metrics properties will be used.	MAIN