Keep comments on `base` properties

Right now base property comments are not merged because the `base` node is simply deleted during merging:

```yaml
# This comment will not be included in lima.yaml
base: template://default
```

A workaround is to add an empty line:

```yaml
# This comment will be copied over

base: template://default
```

It would be nice to retain the comment even without the extra empty line.