dpg, metadata from codegen #2303

Generate resources/generator/metadata.json

Info wish to contain

Swagger

1. input files (all Swaggers)
2. repo and commit id
3. readme file and tag (if available)
4. version of autorest.core, modelerfour, codegen

TypeSpec

1. input files (tsp or the entry file -- client.tsp or main.tsp)
2. repo and commit id
3. version of compiler, typespec-azure-core, tcgc, emitter

Some info likely not able to be provided by emitter along, e.g. "repo and commit id"