Support processing env vars into Secret via libraries like envconfig

[andremarianiello]

I have a config struct with some regular fields and some secret fields, currently represented with string. I parse environment variables into this struct using https://github.com/kelseyhightower/envconfig. If I replace the secret string field with a logfusc.Secret[string], the parsing process no longer populates the field, presumably because it does not know how to decode strings from the environment into logfusc.Secret[string] structs. However, it would be very convenient if this worked like it does when unmarshalling JSON. Could this behavior be added? Ideally it would work for all generic logfusc.Secret[T], but simply supporting logfusc.Secret[string] first would be a big improvement.

This is what I am currently using to work around it

type SecretStringDecoder struct {                              
  logfusc.Secret[string]                                       
}                                                              
                                                               
func NewSecretStringDecoder(value string) SecretStringDecoder {
  return SecretStringDecoder{logfusc.NewSecret(value)}         
}                                                              
                                                               
func (d *SecretStringDecoder) Decode(value string) error {     
  *d = NewSecretStringDecoder(value)                           
  return nil                                                   
}                                                              

but this feels to me like it shouldn't be necessary. What do you think?