Opening this PR off jborean's branch, to run tests (which need to be run on upstream).

Updates the ContainerRegistry authentication logic to work with OCI compliant registries like ghcr.io. The changes skip using the Azure environment credentials unless the bearer service ends with .azurecr.io as these tokens are only useful for ACR. The Azure AccessToken to Bearer token exchange is also simplified with an unecessary step removed.

A new special prefix is used for the username when a credential represents an Azure AccessToken. This is necessary to ensure that only these specific types of credentials will use the Azure specific steps for authentication.

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