[DOCS] Node Stats nodes.fs.io_stats.devices.XXXXX.io_time_in_millis not documented

[stefnestor]

👋🏼 howdy! The Node Stats API does not have information on how to interpret the following two columns which do return in the API (checked v8.1 & v7.x):

• nodes.fs.io_stats.devices.{$COUNT}.io_time_in_millis
• nodes.fs.io_stats.total.io_time_in_millis

"io_stats": {
    "devices": [{
            "device_name": "dm-1",
+            "io_time_in_millis": 7152,
            "operations": 20361,
            "read_kilobytes": 468,
            "read_operations": 58,
            "write_kilobytes": 284356,
            "write_operations": 20303 }],
    "total": {
+        "io_time_in_millis": 7152,
        "operations": 20361,
        "read_kilobytes": 468,
        "read_operations": 58,
        "write_kilobytes": 284356,
        "write_operations": 20303 }}

[elasticmachine]

Pinging @elastic/es-docs (Team:Docs)

[elasticmachine]

Pinging @elastic/es-distributed (Team:Distributed)