[Chronik] Add plugin field to TxInput in tx.py
Summary:
Allows plugins to access the plugin data of the spent inputs from previously ran plugins.
We can get this data cheaply and it makes plugins vastly more powerful as information can flow from transaction to transaction.
Test Plan: cargo test -p chronik-plugin-impl
Reviewers: Fabien, #bitcoin_abc
Reviewed By: Fabien, #bitcoin_abc
Differential Revision: https://reviews.bitcoinabc.org/D16525