Mayya Sharipova 0c68765088
Adds usage stats for vectors ()
Example of usage:

_xpack/usage

"vectors": {
    "available": true,
    "enabled": true,
    "dense_vector_fields_count" : 1,
    "sparse_vector_fields_count" : 1,
    "dense_vector_dims_avg_count" : 100
}
Backport for 
2019-07-31 12:32:41 -04:00
..
2019-07-31 12:32:41 -04:00