Enhance the bundle.ConfigWorkflow and engines.Workflow APIs and clarify the usage

[wyli]

Is your feature request related to a problem? Please describe.
Part of #6641 for the bundle enhancement, currently it's unclear how bundle.ConfigWorkflows and engines.Workflow APIs interact and how the user is expected to build a bundle for many 'non-standard' use cases.

The current example demonstrates a simple supervised segmentation workflow

• https://github.com/Project-MONAI/tutorials/blob/main/bundle/python_bundle_workflow/scripts/train.py

The recommended way of creating a bundle for the flexible workflows still needs to be defined, such as

• New bundle: Pathology MIL classification from WSI  model-zoo#262
• https://github.com/Project-MONAI/model-zoo/tree/dev/models/lung_nodule_ct_detection
• https://github.com/Project-MONAI/research-contributions/blob/main/auto3dseg/algorithm_templates/swinunetr/scripts/train.py

[KumoLiu]

A new tutorial tell user they can define things purely Python code and not have the config files under https://github.com/Project-MONAI/tutorials/tree/main/bundle