[REQ] Feature Request - speed up + simplify sample generation

Created by: spacether

Is your feature request related to a problem? Please describe.

• Local sample generation with ./bin/utils/ensure-up-to-date without batch invocation takes a while, ~15 minutes.
• When users update .sh and .bat files, sometimes they forget to update the json config files
• the .sh/.bat/.json config files offer three ways to do the same thing (provide generator inputs). If we use only one way, that will force our users to update the correct files

Describe the solution you'd like

Desired changes:

• always use batch_mode=True here
• convert all the .sh and .bat files to store their inputs in json or yaml files like https://github.com/OpenAPITools/openapi-generator/blob/master/bin/csharp-petstore-net-40.json
• eliminate the generator specific .sh and .bat files
• perhaps allow passing in a single generator name into ensure-up-to-date to allow generation of individual generators, like the old .sh and .bat files

Describe alternatives you've considered

N/A

Additional context

This ticket was created from a discussion with @jimschubert on Slack