shfmt - support simplifying (`-s`) and minifying flags (`-mn`)

`shfmt` supports [simplifying and/or minifying shell scripts](https://github.com/mvdan/sh/blob/master/cmd/shfmt/shfmt.1.scd#generic-flags). However, there is no support provided via `.editorconfig` for the flags. So we'll need some additional configuration in the shfmt Gradle DSL to enable these.

My thoughts are something akin to one of the following:

Option 1
```gradle
// Provides future extensible flexibility and follows the lead set by the `ktfmt` configuration
spotless {
shell {
shfmt().configure {
it.minify = true
it.simplify = true
}
}
}
```

Option 2
```gradle
// If any other options become available in the future, this seems to be less extensible, however, it is very readable
spotless {
shell {
shfmt()
.minify()
.simplify()
}
}
```

Note that minifying the code implies simplifying the code. So both flags can probably be true, but both flags aren't required to simplify and minify.