[Searchable Snapshot] Expose local file system cache stats into node stats

[aabukhalil]

Referring to #4964

Expose all file system cache stats (usage, activeUsage, hitCount, missCount, ...) into NodeStats API. Stats already exist as POJOs and computed correctly but we need to include them in node stats.

[kotwanikunal]

API: GET <node_url>/_nodes/stats/file_cache

Sample output:

{
    "_nodes": {
        "total": 1,
        "successful": 1,
        "failed": 0
    },
    "cluster_name": "runTask",
    "nodes": {
        "cp-GjpOoRqedOuLwQCW6AQ": {
            "timestamp": 1680203484985,
            "name": "runTask-0",
            "transport_address": "127.0.0.1:9300",
            "host": "127.0.0.1",
            "ip": "127.0.0.1:9300",
            "roles": [
                ...
            ],
            "attributes": {
               ...
            },
            "file_cache": {
                "timestamp": 1680203484985,
                "active_in_bytes": 44426,
                "total_in_bytes": 302562354790,
                "used_in_bytes": 44426,
                "evicted_in_bytes": 0,
                "removed_in_bytes": 0,
                "replaced_count": 124,
                "active_percent": 100,
                "used_percent": 0,
                "cache_hits": 733,
                "cache_miss": 0
            }
        }
    }
}