Feature request: provide smithy build information in metadata in the model when using the run plugin

[mullermp]

The run plugin feature for smithy cli will only pass along the model through standard input. To enable code generators in multiple target languages, it is beneficial for the run plugin to provide access to configuration on the smithy build file, such as library names, versions, and other code generation options. This should either be provided in the model as metadata or an environment variable should provide access to the smithy build json or this metadata.

https://smithy.io/2.0/guides/smithy-build-json.html#run-plugin

I lean towards an option that has an ENV variable that contains a json string of arbitrary metadata that is a sibling to the run plugin. Example, given:

            "plugins": {
                "run::smithy-ruby": {
                    "command": ["smithy-ruby", "smith", "client", "--gem-name=weather", "--gem-version=1.0.0"],
                    "options": {
                        "foo": "bar"
                    }
                }
            }

perhaps ENV['SMITHY_PROJECTION_OPTIONS'] could be '{"foo": "bar"}'?