Allow specifying training epochs when calling `run_cli`

[Francis777]

The number of training epochs seems to be hardcoded to 24 and isn't overwritten anywhere(maybe I'm missing something?), this PR adds a new input argument extra_trainer_config_args to run_cli, I think it's better than directly adding epochs as input because it's more flexible and can be used to specify other trainer args in the future.

The default behavior is unchanged.

[yinchimaoliang]

Thanks for your contribution!