Fix json encode of config for "credentials_issuer" and "authorizer" during import

[stszap]

Related issue

#182

Proposed changes

Use json.RawMessage instead of models.RawMessages because the former is marshaled properly.

Checklist

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• I have added tests that prove my fix is effective or that my feature works
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Further comments

I would be happy to add some tests but not sure how to mock ioutil.ReadFile and newClient() in importCmd.

[aeneasr]

Thank you!