Generate config command

[miriamkw]

Enhance the generate_config command in the CLI:

• Now, if there are some input errors in the prompts, this will not be identified until the user has answered all of the questions, which might be quite frustrating
• Add input validation
• Also, if there is an error, the user has to start all over again. Fix so that there is a second chance to write again instead.
• Option to use either prompts or command line interface
• Update README accordingly

The solution can be to give explanatory error messages immediately after an input error, and reprompting the input field to let users try again from where they left off.

[miriamkw]

From the duplicate issue:

Currently in the generate_config command, it is only possible to use the promts to generate configurations. It should also be an option to generate configs programmatically.

• Add options to generate configs programatically
• Update README accordingly
• How to handle default values in that case? Is it not possible?

[miriamkw]

The callback function in prompts works perfectly - you are reprompted for the input with a descriptive message.

Input validation:

• Config file name: Make it possible to include or exclude the file extension
• Input data: same as config
• Prediction horizons: Must be comma separated lists of ints.
• Lagged features: Must be an integer >=0
• Num features and cat features: comma separated lists of strings