Get training and inference datasets from S3

[momegas]

Is your feature request related to a problem? Please describe.
At the moment, whitebox only accepts the training dataset and inferences through the API. In order to load data faster, users should be able to define how whitebox can retrieve this data from an SQL database.

Describe the solution you'd like
In the UI / API / SDK the user should be able to choose a source for the model training dataset and inferences. A possible flow is the following:

1. Create the model (either through UI or SDK)
2. Go to settings and select where the data will be coming from (S3, in the future SQL, etc)
3. Add the required credentials for S3 bucket and the corresponding file

Describe alternatives you've considered
At the moment, whitebox only accepts the training dataset and inferences through the API. This is an alternative but we need to extend it.

Additional context
Here is an exmaple of how Aporia does something similar: https://docs.aporia.com/introduction/quickstart