Being able to choose ExtensionAppTokenRepository implementation on BDK creation

[Djoe-Denne-Symph]

Feature Request

Description of Problem:

We are deploying several instance of the same bot (more Extension app Backend in our case) for High Availability reason.
Unfortunatly with an In Memory repository for the ExtApp token, the Circle Of Trust can fail. In fact, if the bot instane that initiate the CoT is not the same all the long is not the same it will fail due to one of the token stored to validate the authentication will not be accessible.

To fix that we will implement our own Mongo repository. but there is no way to say to BDK wich instance of ExtensionAppTokenRepository we want to use.

When I create my Bdk instance I want to pass the implementation of ExtensionAppTokenRepository I want

Potential Solutions:

Add a new construction in AuthenticatorFactory to be able to pass the ExtensionAppTokenRepository implementation we want to use