Revise the PGXN Meta Spec to:

• Classify types of extensions (CREATE EXTENSION extensions, loadable modules, applications, services, TLEs, etc)
• Support automated binary packaging with various build pipelines, Postgres versions, platforms, and architectures
• Support third-party dependency specification, and some pattern to automatically satisfy those dependencies

Then implement a library to support the v1 and v2 specs, migrate v1 data to v2, and to merge multiple v2 specs (so that the build system can overlay additional metadata)