implement quick and robust story fingerprinting

[wochinge]

Description of Problem:
We are fingerprinting the stories here, to ensure that we skip re-training the models in case the training data didn't change.

• This is not robust due to model is retrained everytime due to dynamic checkpoint names #4612
• This is slow as it dumps all stories as yaml to get the hash of the string.

Overview of the Solution:

Definition of Done:

• Fingerprinting stories is quick (e.g. takes less than 30 seconds for the multiwoz dataset)
• the fingerprint stays stable with OR statements and checkpoints across different runs