make the sdk a separate module

The SFTPGo SDK now is at the following URL

https://github.com/sftpgo/sdk

Fixes #657

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

kms/basesecret.go

@@ -1,7 +1,7 @@
 package kms
 
 import (
-	sdkkms "github.com/drakkan/sftpgo/v2/sdk/kms"
+	sdkkms "github.com/sftpgo/sdk/kms"
 )
 
 // BaseSecret defines the base struct shared among all the secret providers

kms/builtin.go

@@ -9,7 +9,7 @@ import (
 	"errors"
 	"io"
 
-	sdkkms "github.com/drakkan/sftpgo/v2/sdk/kms"
+	sdkkms "github.com/sftpgo/sdk/kms"
 )
 
 var (

kms/kms.go

@@ -8,8 +8,9 @@ import (
 	"strings"
 	"sync"
 
+	sdkkms "github.com/sftpgo/sdk/kms"
+
 	"github.com/drakkan/sftpgo/v2/logger"
-	sdkkms "github.com/drakkan/sftpgo/v2/sdk/kms"
 )
 
 // SecretProvider defines the interface for a KMS secrets provider

kms/local.go

@@ -7,10 +7,9 @@ import (
 	"encoding/hex"
 	"io"
 
+	sdkkms "github.com/sftpgo/sdk/kms"
 	"gocloud.dev/secrets/localsecrets"
 	"golang.org/x/crypto/hkdf"
-
-	sdkkms "github.com/drakkan/sftpgo/v2/sdk/kms"
 )
 
 func init() {