Option to require env vars to be set and not empty by default

It looks like there is no way to require env vars to be set and not empty by default?

https://go.dev/play/p/fiRtVlFW3if
```
package main

import (
"fmt"

"github.com/caarlos0/env/v10"
)

func main() {
type Config struct {
Username string `env:"EX_USERNAME" envDefault:"admin"`
Password string `env:"EX_PASSWORD"`
}

var cfg Config
if err := env.ParseWithOptions(&cfg, env.Options{
Environment: map[string]string{
"EX_USERNAME": "https://google.com",
"EX_PASSWORD": "",
},
RequiredIfNoDef: true,
}); err != nil {
fmt.Println(err)
}

fmt.Printf("%+v\n", cfg)
}
```

Results in
```
{Username:https://google.com Password:}

Program exited.
```

Start with ParseWithOptions and the RequiredIfNoDef option, using the example in the issue as the reproduction case. Determine how an explicitly empty EX_PASSWORD is handled when required variables have no defaults. Done means the parser can require such values by default and the behavior is covered by tests.

Written by the indexing model from the issue text.