[Feature request] Ability to configure keySeparator for project (for JSON export)

[Qt1Rbt]

Hi,

Some project I work on historically uses plain English sentences as translation key (and thus set keySeparator to false in i18next config). Others projects uses custom keySeparators.

It would be great to have a global project setting to define the keySeparator, with the added flexibility to override it per translation if needed.

Currently:
"Exemple. This is a key"

is exported as:
{ "Exemple": { "This is a key": "The translation" } }

however, when keySeparator is set to a value other than ".", we expect the output to remain:
{ "Exemple. This is a key": "The translation" }

This feature may not be applicable to all formats, but it would be especially helpful in our case and for frameworks like i18next.