feat: allow authz granters to specify forwarding info for token trans…

…fer (#6661)

* First attempt to modify proto and validation.

* Fmt

* Make it compile

* Proto

* Add basic validation

* Added tests

* Fix nil check and remove redundant code.

* Move "forwarding" to non-pointer

* Added one test case.

* Moved error and changed method name.

* PR Feedback.

* Add nullable=false

* Added test and fixed test names

* Run make proto-all

* Change pointer to non-pointer

* Change Yet Another Pointer

* More pointers

* Comments and naming

* Reintroduce brace removed while merging

* Remove accidentally reintroduced tests