feat: resource keys and service credentials

[shemau]

Description

#253

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[shemau]

This pull request is a first pass. It requires additional work, including tests and ibm_catalog.json updates which have not been started yet.

The new code is copied from terraform-ibm-cos for consistency and extended to support two services.

I will looking for guidance on providing two separate sets of outputs, by service; or one combined set of outputs. The combined set of outputs covering both services may be more consistent with other modules. The separate outputs may be good for something.