[OpenAPI] Allow configuration of where to pull openapi-generator from

[phatcher]

Description of the enhancement:
People may have forked/modified the openapi-generator or need to test the code generator, so just using the public released version is not sufficient.

Proposed solution:
Allow the user to configure where to aquire the openapi-generator instance.

[keithchong]

Thanks for opening this Paul.

FWIW, the Eclipse version has an env var that you can set to point to a generator jar. (Start eclipse with -Dorg.eclipse.codewind.openapi.cli.jar.path).

There is no option like this yet for the VS Code plugin.

Ref: eclipse-archived/codewind-openapi-vscode#65

[phatcher]

Thanks for the update, it was pure self-interest as I've just updated the code generator and it would be nice to use it from VS Code rather than java/command line

See openapi-generator #6025

Is the VS Code plugin open source, doesn't sound like a big change, I can also see other requirements like being able to specify where the templates are sourced from.