Improve asset versioning task
Improve asset versioning task

Added:
- Support for writing multiple times to the same file.
- Support for random hexadecimal value instead of timestamp.

Usage:

```json
"versions": [
    {
        "format": "timestamp",
        "key": "now",
        "outfile": "./assets.json"
    },
    {
        "format": "hex:8",
        "key": "hex",
        "outfile": "./assets.json"
    }
]
```

```json
{
    "now": 1665071717350,
    "hex": "6ef54181c4ba"
}
```

locomotivemtl/locomotive-boilerplate,locomotivemtl/locomotive-boilerplate