Provide a migration system from Hibernate to ElasticSearch

When nuxeo-elasticsearch-audit is deployed it will automatically replace the default JPA implementation. However, if you have previous data inside JPA you have to migrate it. The migration is done in a Worker that will simply go through all existing JPA Audit entries to store them inside the Elasticsearch index. The migration is done using a configurable batch size (default is 1000 entries). An Automation Operation is provided to trigger the migration Work. Sample call using curl : curl -H 'Content-Type:application/json+nxrequest' -X POST -d '{"params":{"batchSize":5000}}' -u Administrator:Administrator http://nuxeoserver:8080/nuxeo/api/v1/automation/Audit.StartMigration NB : Migration of 16 Millions entries on a C3.XLarge AWS instance with default PGSQL setup and default embedded Elasticsearch takes about 2h30 (1800 entries/s).