[Cashtab] Add function to generate burn targetOutputs
Summary:
Add function intended to deprecate cashMethods generateBurnOpReturn as part of transaction construction refactors
This diff does not yet implement the function
Test Plan: npm test
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Subscribers: Fabien
Differential Revision: https://reviews.bitcoinabc.org/D15100