User can add new stats method in dataset summary / analyzer

[mingxin-zheng]

Is your feature request related to a problem? Please describe. User may need customized functions so that they can have their own statistic metric in dataset_summary/data_analyzer.

Describe the solution you'd like Reference link for a potential: https://github.com/Project-MONAI/MONAI/pull/4765#discussion_r943427586

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

Additional context Add any other context or screenshots about the feature request here.