Describe the bug

Unless I'm mistaken, the env resets automatically when an episode is over, which means the terminal observation is not accessible to the agent which prevent from doing proper bootstrapping for infinite horizon problems.

See openai/gym#2484 and openai/gym#1632

Expected behavior

openai/gym#2484

Reason and Possible fixes

Add terminal_observation key to the info dict, as already done for the timelimit truncation.

Checklist

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