Add Support for Azure WAL-G Backups (#1537)

This commit adds support for using an Azure storage account as a backup
location.

It uses the existing GCS functionality as a reference for what to do,
and follows the example set by GCS as closely as possible.

The decision to name the cloud provider key "aws_or_gcp" is unfortunate
while adding support for Azure, but I have left it alone to allow for
this changeset to be backwards compatible.

pkg/apis/acid.zalan.do/v1/operator_configuration_type.go

@@ -132,6 +132,7 @@ type AWSGCPConfiguration struct {
 	AWSRegion                    string `json:"aws_region,omitempty"`
 	WALGSBucket                  string `json:"wal_gs_bucket,omitempty"`
 	GCPCredentials               string `json:"gcp_credentials,omitempty"`
+	WALAZStorageAccount          string `json:"wal_az_storage_account,omitempty"`
 	LogS3Bucket                  string `json:"log_s3_bucket,omitempty"`
 	KubeIAMRole                  string `json:"kube_iam_role,omitempty"`
 	AdditionalSecretMount        string `json:"additional_secret_mount,omitempty"`