fix: don't start operator if `last_processed_batch_filepath` isn't provided

[MarcosNicolau]

Changes If last_processed_batch_filepath is not provided on the operator config, then don't start the program. This is to make sure operator owners don't forget to pass this new field. Alternatively, we could create a default file but I am not sure about how that could go.

Testing Remove the last_processed_batch_filepath from the operator config and you should see an err indicating the missing field.

Closes #1209