Enhancement: Support `options` field on `/sys/mounts` 

Right now, there's no way of performing certain logic based on if the `kv` endpoint is 1 or 2. 

I think this is just a case of adding 

```ruby
# @!attribute [r] options
    #   Options of the mount.
    #   @return [String]
    field :options
```

to the `lib/vault/api/sys/mount.rb` file