Missing float field HTML5 validation

[cimbalo]

Float field are rendered as text input and have no HTML5 validation on submit.
This permit to submit non numerical values for a float field.

I think the following definition are missing in lib/rails_admin/config/fields/types/float.rb

register_instance_option :view_helper do
  :number_field
end

register_instance_option :html_attributes do
  {
    required: required?,
    step: "any",
  }
end

This will change the rendered field from:
<input class="form-control" type="text" [...]>
to:
<input class="form-control" step="any" type="number" [...]>

If this issue is confirmed I can make a PR for it.

Edit: added 'required' attribute