* updating `github.com/Azure/azure-sdk-for-go` to `v45.0.0`
* updating `github.com/Azure/go-autorest` to `v0.11.3`
* updating `github.com/hashicorp/go-azure-helpers` to `v0.12.0`
* updating `github.com/tombuildsstuff/giovanni` to `v0.12.0`
* Upgrading to 2.0.0 of github.com/hashicorp/go-azure-helpers
* Support for authenticating using Azure CLI
* backend/azurerm: support for authenticating using the Azure CLI
* vendor updates
- updating to v21.3.0 of github.com/Azure/azure-sdk-for-go
- updating to v10.15.4 of github.com/Azure/go-autorest
- vendoring github.com/hashicorp/go-azure-helpers @ 0.1.1
* backend/azurerm: refactoring to use the new auth package
- refactoring the backend to use a shared client via the new auth package
- adding tests covering both Service Principal and Access Key auth
- support for authenticating using a proxy
- rewriting the backend documentation to include examples of both authentication types
* switching to use the build-in logging function
* documenting it's also possible to retrieve the access key from an env var