fix: Return API secret from createAccountsKeys - Fixes #82

[kenske]

Fixes

Fixes https://github.com/twilio/terraform-provider-twilio/issues/82

Checklist

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• [ ] I have made a material change to the repo (functionality, testing, spelling, grammar)
• [ ] I have read the Contribution Guidelines and my PR follows them
• [x] I have titled the PR appropriately
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• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added the necessary documentation about the functionality in the appropriate .md file
• [ ] I have added inline documentation to the code I modified

If you have questions, please file a support ticket, or create a GitHub Issue in this repository.

[childish-sambino]

Note that this change is to generated code which would be reverted on the next release.

Changes are needed in https://github.com/twilio/twilio-oai-generator/ to properly render this change.

I've bumped this issue internally (ref DI-2321).