Save locale information on NextJS middleware

[twistershark]

We want to create a new cookie called SWC_LOCALE which will represent the current locale of the pages the user is visiting.

Whenever a user visits a page, our middleware should check if SWC_LOCALE exists. If it doesn't exist, we create SWC_LOCALE with the corresponding locale. Whenever a user visits a page in a different locale compared to what is saved in the SWC_LOCALE, we update the cookie in our middleware since this information will be used as metadata in Mixpanel, Sentry and everywhere else needed.