Introduce external-internal token exchange provider

We may need dedicated token-exchange provider for external-internal token exchange.

Similarly like we have token-exchange provider for standard token-exchange, it can be good to introduce new provider for external-internal token exchange V2, so we can keep the existing V1 (for backwards compatibility), but address use-cases for supported external-internal in V2.
It could be experimental by default.
We should make sure that it does not break/update existing capabilities of V1 provider.
Will be good to have dedicated provider just for external-internal and then later introduce dedicated provider for internal-external. Using same provider for both external-internal and internal-external token exchange is likely not very beneficial as those implementations are doing completely different things (Actually they are both more close to internal-internal token exchange as external-internal may have likely same/similar rules for issuing new token and internal-external may have same/similar rules for the validation of internal token). Also it allows us to first focus on supported "External internal" and then later on supported "internal external" instead of trying to address both together.

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