This adds a some scaffolding for Python-based plugins using PyO3 for Chronik.
Currently, this only finds the Python version and logs it. The purpose is to setup the build and CI so we can optionally add plugins using the `BUILD_BITCOIN_CHRONIK_PLUGINS` flag.
The goal is to load Python scripts from a `plugins` folder in the datadir, which specify which LOKAD ID to index, and provide functions that will be called by Chronik on txs that match the LOKAD ID, which will then be indexed using GroupHistoryWriter and GroupUtxosWriter into either column families for that plugin, or into column families shared by all plugins (and prefixed appropriately).
Users can then call `/plugin/<plugin name/id>/history/confirmed-txs/unconfirmed-txs/utoxs` and get the txs of the protocol specified by the plugin.
One obvious application would be the SLPAgora or SLPDEX contracts, or something similar for ALP, allowing users to fetch all available trades for a given token ID or pubkey.