Use Multiple Bundle Config Files With Inference/Training

Is your feature request related to a problem? Please describe.
One of the best practice concepts we're documenting with bundles is having a config file with common definitions used by inference or training configs. This would be "common.json" or "common.yaml", and would for example be loaded first before "inference.json" or "train.json". MONAILabel currently loads only one file and optionally will load "multi_gpu_train.json/yaml", if "common.json/yaml" is present would follow best practice to load this file first.

Describe the solution you'd like
The bundle infer or train tasks should load "common.json/yaml" before infer/train configs. This should be included in the constants data structures used by these tasks to track what files are searched for. This behaviour should also be clearly documented.

Describe alternatives you've considered
Currently definitions have to be duplicated across multiple scripts to ensure compatibility with MONAILabel. This is error-prone and not modular.

Additional context
This is an important change I feel in conjunction with the bundle work we're doing for the 1.3 core release.

Locate the bundle inference and training task entry points and their constants or data structures that track searched config files. Trace how multi_gpu_train and the existing config files are loaded, then review the bundle documentation. Done means common.json/yaml is loaded before the inference or training config and the behavior is documented.