Fix OpenAPI tag configuration

[srchase]

Fixes bug in OpenAPI tag configuration where tags were not passed through without being explicitly set in the list of supported tags.

The corrected behavior for each smithy-build.json config:

• Passes through all tags:

{
    "version": "1.0",
    "plugins": {
        "openapi": {
            "service": "smithy.example#Weather",
            "tags": true
        }
    }
}

• Passes through only tags that have been configured as supported (e.g. foo and bar):

{
    "version": "1.0",
    "plugins": {
        "openapi": {
            "service": "smithy.example#Weather",
            "tags": true,
            "supportedTags": ["foo", "bar"]
        }
    }
}

• Does not pass through tags, as list of supported tags is empty:

    "version": "1.0",
    "plugins": {
        "openapi": {
            "service": "smithy.example#Weather",
            "tags": true,
            "supportedTags": []
        }
    }
}

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.