Replace `past` with `past_key_values`
# What does this PR do?
The argument `past` was completely replaced with `past_key_values` thus this PR should fix any problem with `kwargs` being swallowed for old models in generation. 
Related to #20347
_The documentation is not available anymore as the PR was closed or merged._<|||||>Ok the failing tests were because I did not pull from main, were the `tf_utils` now uses the `generate_config`. LGTM the failing test seems to be unrelated<|||||>Yes, good to merge for me!