Optionally enable actuation in `physics.after_reset`?

Would it make sense to optionally enable actuation in the `after_reset` method [here](https://github.com/google-deepmind/dm_control/blob/main/dm_control/mujoco/engine.py#L310)?

The use case I have in mind is initializing episode with actuators in a certain activation state `physics.data.act`, before any control input is provided. What do you think?

Start by reading the after_reset method in dm_control/mujoco/engine.py at the linked location, along with the surrounding reset behavior. Determine how an optional actuation path could initialize physics.data.act before control input while preserving the current default behavior; the issue is complete when that behavior is defined and implemented consistently.

Written by the indexing model from the issue text.