Add MaxNoncurrentVersions to NoncurrentExpiration action (#13580)

This unit allows users to limit the maximum number of noncurrent 
versions of an object.

To enable this rule you need the following *ilm.json*
```
cat >> ilm.json <<EOF
{
    "Rules": [
        {
            "ID": "test-max-noncurrent",
            "Status": "Enabled",
            "Filter": {
                "Prefix": "user-uploads/"
            },
            "NoncurrentVersionExpiration": {
                "MaxNoncurrentVersions": 5
            }
        }
    ]
}
EOF
mc ilm import myminio/mybucket < ilm.json
```

cmd/storage-datatypes.go

@@ -93,7 +93,8 @@ type FileInfoVersions struct {
 	// latest version.
 	LatestModTime time.Time `msg:"lm"`
 
-	Versions []FileInfo `msg:"vs"`
+	Versions     []FileInfo `msg:"vs"`
+	FreeVersions []FileInfo `msg:"fvs"`
 }
 
 // findVersionIndex will return the version index where the version