Create Index Backup

1. ​GET https://opensolr.com/solr_manager/api/create_backup
2. Parameters:
   1. ​email - your opensolr registration email address
   2. api_key - your opensolr api_key
   3. ​core_name - the name of the core you wish to create a backup for

3. Example: https://opensolr.com/solr_manager/api/create_backup?email=PLEASE_LOG_IN&
   api_key=PLEASE_LOG_IN&core_name=my_solr_core