support `-f` and `--no-prune` for rmi command

There is nerdctl help of rmi:
```
$ nerdctl rmi --help
NAME:
nerdctl rmi - Remove one or more images

USAGE:
nerdctl rmi [command options] [flags] IMAGE [IMAGE, ...]

OPTIONS:
--help, -h show help (default: false)
```
And docker help of rmi is:
```
$ /usr/local/bin/docker rmi --help

Usage: docker rmi [OPTIONS] IMAGE [IMAGE...]

Remove one or more images

Options:
-f, --force Force removal of the image
--no-prune Do not delete untagged parents
```

Please notice that there is no `--force` and `--no-prune` at `nerdctl rmi`. Could we add those flags?