file: provide user name and group name lookups for stat listings

file: provide user name and group name lookups for stat listings

This provides more user friendly information than numeric IDs.

Before this patch:

ubus call file list '{"path":"/proc"}'
...
{
	"name": "kcore",
	"type": "file",
	"size": 140737471586304,
	"mode": 33024,
	"atime": 1764716086,
	"mtime": 1764716086,
	"ctime": 1764716086,
	"inode": -268435271,
	"uid": 0,
	"gid": 0,
},
...

After this patch:

ubus call file list '{"path":"/proc"}'
...
{
	"name": "kcore",
	"type": "file",
	"size": 140737471586304,
	"mode": 33024,
	"atime": 1764716086,
	"mtime": 1764716086,
	"ctime": 1764716086,
	"inode": -268435271,
	"uid": 0,
	"gid": 0,
	"user": "root",
	"group": "root"
},
...

Tested on: OpenWrt SNAPSHOT r32139-1f879b8839 / 6.12.59
Signed-off-by: Paul Donald <[email protected]>
Link: https://github.com/openwrt/rpcd/pull/22
Signed-off-by: Robert Marko <[email protected]>