Add RealApp support for Decision Tree

[zyteka]

For this issue, Decision Tree explainers should be supported in RealApp, and the plot_tree function should be updated to have the consistent visualization format.

For the explanation format, consider: https://scikit-learn.org/stable/auto_examples/tree/plot_unveil_tree_structure.html

[zyteka]

Moving this to new milestone to avoid blocking sibyl-api