Exposes a few metrics for Prometheus under /metrics if started with --prometheus.
Example:
# HELP rest_server_blob_read_bytes_total Total number of bytes read from blobs
# TYPE rest_server_blob_read_bytes_total counter
rest_server_blob_read_bytes_total{repo="test",type="data"} 2.13557024e+09
rest_server_blob_read_bytes_total{repo="test",type="index"} 1.198653e+06
rest_server_blob_read_bytes_total{repo="test",type="keys"} 5388
rest_server_blob_read_bytes_total{repo="test",type="locks"} 1975
rest_server_blob_read_bytes_total{repo="test",type="snapshots"} 10018
# HELP rest_server_blob_read_total Total number of blobs read
# TYPE rest_server_blob_read_total counter
rest_server_blob_read_total{repo="test",type="data"} 3985
rest_server_blob_read_total{repo="test",type="index"} 21
rest_server_blob_read_total{repo="test",type="keys"} 12
rest_server_blob_read_total{repo="test",type="locks"} 12
rest_server_blob_read_total{repo="test",type="snapshots"} 32
# HELP rest_server_blob_write_bytes_total Total number of bytes written to blobs
# TYPE rest_server_blob_write_bytes_total counter
rest_server_blob_write_bytes_total{repo="test",type="data"} 1.063726179e+09
rest_server_blob_write_bytes_total{repo="test",type="index"} 395586
rest_server_blob_write_bytes_total{repo="test",type="locks"} 1975
rest_server_blob_write_bytes_total{repo="test",type="snapshots"} 1933
# HELP rest_server_blob_write_total Total number of blobs written
# TYPE rest_server_blob_write_total counter
rest_server_blob_write_total{repo="test",type="data"} 226
rest_server_blob_write_total{repo="test",type="index"} 6
rest_server_blob_write_total{repo="test",type="locks"} 12
rest_server_blob_write_total{repo="test",type="snapshots"} 6
If htpasswd was modified, it will be automatically reloaded. This check
happens at most once per second and only on incoming requests.
Note that this removes the public `NewHtpasswd()` function.
