Update the GNN encoding for XGB financial example

[ZiyueXu77]

Fixes previous result where GNN encoding performs worse than raw feature

Description

GNN encoding is supposed to be used as secondary complementary features, rather than by itself, changing the behavior

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Quick tests passed locally by running ./runtest.sh.
• In-line docstrings updated.
• Documentation updated.

[ZiyueXu77]

/build

[YuanTingHsieh]

LGTM, great changes, the GNN is for more feature engineering

[YuanTingHsieh]

/build