Add parseMissingKeyHandler like in i18n react

[tokomeno-kaltura]

https://www.i18next.com/overview/configuration-options#missing-keys

Can't add parseMissingKeyHandler like I used to do with react-i18next

[aralroca]

did you try the logger from our configuration? https://github.com/aralroca/next-translate#3-configuration Is a function to log the missing keys in development and production