Add ways to configure "default" value for training data limit

[gkumbhat]

Description

Currently we are allowing users to set default value per module per model for training data limit. However, its easier for users to configure a default for all modules or for all models in a module. So something like:

training_data_limit:
    default: 1000000
    <module-id>:
        default: 100
        <model-name>: 100