feat: set filtering state of select

[PJGaetan]

This PR adresse the following issue #173

It allows allows use the select where the filter mode is activated when Run starts.

Thanks for telling me to also update the focus @maaslalani !

I have the following results with this code (readme example adapted a little).

package main

import (
	"fmt"

	"github.com/charmbracelet/huh"
)

func main() {
	var country string
	s := huh.NewSelect[string]().
		Title("Pick a country.").
		Filtering(true).
		Options(
			huh.NewOption("United States", "US"),
			huh.NewOption("Germany", "DE"),
			huh.NewOption("Brazil", "BR"),
			huh.NewOption("Canada", "CA"),
		).
		Value(&country)

	huh.NewForm(huh.NewGroup(s)).Run()

	fmt.Println("You chose ", country)
}