Cut down on parsing time for large projects

[joshcarp]

Purpose

Currently parsing times of large projects can be upwards of 20 seconds, which is unacceptable with tools like sysl-catalog which has a live-reloading feature. Parsing times need to be cut down eventually

Suggested approaches

Allow ability to import sysl json files

A majority of sysl in a lot of projects is generated from imports (swagger/openapi or protos with sysl-catalog).
Instead of generating sysl source code, they could generate sysl json. This would use the protobuf json library to output json representation of the sysl proto objects instead of sysl source code.

import index.json ~pb # sysl json NOT openapi