Ensure Azure access and secret keys are JSON in Workhorse config.toml

What does this MR do?

This mirrors the change made to fix AWS access and secret key rendering with AWS in !2639 (merged).

We probably will never hit a failure with Azure as we did with S3 because there are no third-party options for Azure Blob Storage. In addition, https://docs.microsoft.com/en-us/azure/storage/common/storage-account-overview says:

Storage account names must be between 3 and 24 characters in length and may contain numbers and lowercase letters only.

The access key is also a base64-encoded value of binary data, so it won't have any special characters.

Related issues

Follow-up to !2639 (merged).

Checklist

See Definition of done.

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• Test plan indicating conditions for success has been posted and passes
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