Add support for Azure Blob Storage (#171)

* Scaffold Azure storage backend that does nothing yet

* Implement copy for Azure Blob Storage

* Set up automated testing for Azure Storage

* Implement pruning for Azure blob storage

* Add documentation for Azure Blob Storage

* Add support for remote path

* Add azure to notifications doc

* Tidy go.mod file

* Allow use of managed identity credential

* Use volume in tests

* Auto append trailing slash to endpoint if needed, clarify docs, tidy mod file

cmd/backup/script.go

@@ -15,6 +15,7 @@ import (
 	"time"
 
 	"github.com/offen/docker-volume-backup/internal/storage"
+	"github.com/offen/docker-volume-backup/internal/storage/azure"
 	"github.com/offen/docker-volume-backup/internal/storage/local"
 	"github.com/offen/docker-volume-backup/internal/storage/s3"
 	"github.com/offen/docker-volume-backup/internal/storage/ssh"
@@ -76,6 +77,7 @@ func newScript() (*script, error) {
 				"WebDAV": {},
 				"SSH":    {},
 				"Local":  {},
+				"Azure":  {},
 			},
 		},
 	}
@@ -189,6 +191,21 @@ func newScript() (*script, error) {
 		s.storages = append(s.storages, localBackend)
 	}
 
+	if s.c.AzureStorageAccountName != "" {
+		azureConfig := azure.Config{
+			ContainerName:     s.c.AzureStorageContainerName,
+			AccountName:       s.c.AzureStorageAccountName,
+			PrimaryAccountKey: s.c.AzureStoragePrimaryAccountKey,
+			Endpoint:          s.c.AzureStorageEndpoint,
+			RemotePath:        s.c.AzureStoragePath,
+		}
+		azureBackend, err := azure.NewStorageBackend(azureConfig, logFunc)
+		if err != nil {
+			return nil, err
+		}
+		s.storages = append(s.storages, azureBackend)
+	}
+
 	if s.c.EmailNotificationRecipient != "" {
 		emailURL := fmt.Sprintf(
 			"smtp://%s:%s@%s:%d/?from=%s&to=%s",