Implement structure substitute

[hunterhector]

Is your feature request related to a problem? Please describe. Structure substitution is a general family of methods in data augmentation. https://home.ttic.edu/~freda/paper/shi2021substructure.pdf

Behind the scene, the method focuses on replacing sub-structures like phrases or trees from a sentence. This fits very well into Forte's data augmentation framework, where the systems allow one to replace content but keeping the original annotation.

Describe the solution you'd like

1. Implement structure substitution as a ReplacementOp.
2. A pipeline needs to be run to collect the sub-structure statistics first.
3. Structured constraints (as mentioned in the paper) can be considered as the configurations for the processor

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.