feat(security): generating random string with crypto rand

[Mmx233]

The library math/rand is not suitable for high-security scenarios.

Tested with code:

package main

import (
	"fmt"
	"github.com/alist-org/alist/v3/pkg/utils/random"
)

func main() {
	str := random.String(10)
	fmt.Println(str)
}

Output:

# go run .\main.go
IoQrBB5BR4
# go run .\main.go
yDMJVfJqED