[FEATURE REQUEST] Extend AutoTrain API with Start Training Request

[andreasmartin]

Feature Request

Enhance the AutoTrain API by adding a request for starting training (e.g., POST start_training). This request could be similar to the existing POST create_project, but utilize the current environment (such as on HF Spaces).

Motivation

Allowing the use of an already-running instance for training.

Additional Context

No response