Can't set HTML attribute step to "any"

[Step](https://github.com/maxence-charriere/go-app/blob/8bbfa52785b708e2a0e725315f2d306dfcc32d39/pkg/app/html_gen.go#L25507-L25508) is currently defined as:
```go
// Specifies the interval between permissible values for an input field.
Step(v float64) HTMLInput
```
But there is a special value "any" that allows for any value
