Add credentials to registry resource

[joshuastern]

Description

We use external registries that require credentials. This PR is adding access_key, access_secret and credential_type to the harbor_registry resource so that such registries can be managed by terraform.

Acceptance tests

• Have you added an acceptance test for the functionality being added?
• Have you run the acceptance tests on this branch?

Documentation

• Have you create or updated the provider documentation at ./documentation/provider_doc?
  • If new resources or datasource documentation happen, did you add this to the mkdocs.yml configuration?

References

Community Note

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