Add Native Introspection

[monsterbitar]

I think you should consider established opcodes in other bitcoin derived chains as possible ways forward for UTXO based covenants.

The benefits are:

1) You already got a testnet 2) Opcodes demonstrated secure in the wild 3) Free documentation 4) Better compatibility with existing chains 5) Existing testing frameworks

Here's a link to technical specification, same document has abstracts, motivation etc:

https://documentation.cash/protocol/forks/chips/2022-05-native-introspection-opcodes.html#technical-specification

[stevenroose]

This is already present: https://covenants.info/proposals/direct-introspection/