feat: add redirectStatusCode option

[Matiyeu]

This PR add ability to customize the status code to redirect unprefixed route to the default locale(when strategy: prefix) or default locale to unprefixed route (when strategy: prefix_and_default)

example :

{
  strategy: 'prefix',
  redirectStatusCode: 301
}

domain.com => 301 => domain.com/en
domain.com/about-us => 301 => domain.com/en/about-us

[rchl]

I don't like how generic this setting is named and at the same time not explaining exactly what it does. To average user it won't be clear in what circumstances this redirect applies without analyzing the code.

But probably the bigger problem is that in most cases it wouldn't be safe to override this setting and people might corner themselves into issues because of using it.

For example with this option configured to respond with 301, if someone comes to a site and gets redirected from an english to german locale but then wants to manually switch to english then it won't be possible because the browser will force-redirect back to german.

I think that an option like this would only make sense if it only applied in more specific cases where it would be appropriate. For example when the URL that triggered the redirect is 404. And it shouldn't apply if the redirect was due to auto-detecting browser locale as then the user might want to switch back to locale that it redirected from.
But that would require more serious changes in the logic.