[Feature] Async collection within trainers

[vmoens]

Stack from ghstack (oldest at bottom):

• -> [Feature] Async collection within trainers #3173
• [Trainers] SAC Trainer and algorithms #3172
• [Feature] Collectors' getattr_policy and getattr_env #3171
• [Feature] track_policy_version in collectors.py #3170
• [Typing] Edit wrongfully set str type annotations #3169

[pytorch-bot]

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