Allow session refreshing even if the frontend thinks that the session doesn't exist

[rishabhpoddar]

Ths need for this comes when someone is using us only for session recipe and another auth provider for login. In this case, the other auth provider would do a callback to this user's API layer directly which would create a new supertokens session.

In this case, the httpOnly session cookies would be correctly set, but since there are no frontend interceptors (since the auth provider made this API call directly), the frontend would either:

1. Not have sIRTFrontend
2. Have sIRTFrontend with the value of remove.

In case of (1), when the frontend would call doesSessionExist, it would call the refresh API and it would all work fine. But in case of (2), doesSessionExist would return false. The only way to then make the frontend realise that the session actually exists is to manually clear the sIRTFrontend cookie and then call doesSessionExist.

So we should expose a function that does this - something like doesSessionExistCheckUsingBackendCall, and then document that accordingly.