oraclecloud DNS provider should use common way for authentication

[ITD27M01]

• [x] Yes, I'm using a binary release within 2 latest releases.
• [x] Yes, I've searched similar issues on GitHub and didn't find any.
• [x] Yes, I've included all information below (version, config, etc).

What did you expect to see?

Standard way to configure Oracle Cloud tools and SDK is ~/.oci/config where basic configuration information present, like user credentials and tenancy OCID: https://docs.oracle.com/en-us/iaas/Content/API/Concepts/sdkconfig.htm

You can create multiple profiles with different values for these entries, then you can specify which profile to load.

What did you see instead?

Own environment variables for authentication configuration: https://go-acme.github.io/lego/dns/oraclecloud/

As a result it is difficult to use common ~/.oci/config for all the automation (oci terraform as well as acme terraform)

The good example is Designate OpenStack provider where you can specify profile from common clouds.yaml: https://go-acme.github.io/lego/dns/designate/