MM-36271: Bump major version to 6.0 (#17973)

https://mattermost.atlassian.net/browse/MM-36271

```release-note
We bump the major version to 6.0
```

services/users/helper_test.go

@@ -12,11 +12,11 @@ import (
 	"sync"
 	"testing"
 
-	"github.com/mattermost/mattermost-server/v5/app/request"
-	"github.com/mattermost/mattermost-server/v5/config"
-	"github.com/mattermost/mattermost-server/v5/model"
-	"github.com/mattermost/mattermost-server/v5/services/cache"
-	"github.com/mattermost/mattermost-server/v5/store"
+	"github.com/mattermost/mattermost-server/v6/app/request"
+	"github.com/mattermost/mattermost-server/v6/config"
+	"github.com/mattermost/mattermost-server/v6/model"
+	"github.com/mattermost/mattermost-server/v6/services/cache"
+	"github.com/mattermost/mattermost-server/v6/store"
 )
 
 var initBasicOnce sync.Once

services/users/main_test.go

@@ -7,8 +7,8 @@ import (
 	"flag"
 	"testing"
 
-	"github.com/mattermost/mattermost-server/v5/shared/mlog"
-	"github.com/mattermost/mattermost-server/v5/testlib"
+	"github.com/mattermost/mattermost-server/v6/shared/mlog"
+	"github.com/mattermost/mattermost-server/v6/testlib"
 )
 
 var mainHelper *testlib.MainHelper

services/users/password.go

@@ -7,7 +7,7 @@ import (
 	"errors"
 	"strings"
 
-	"github.com/mattermost/mattermost-server/v5/model"
+	"github.com/mattermost/mattermost-server/v6/model"
 	"golang.org/x/crypto/bcrypt"
 )
 

services/users/password_test.go

@@ -10,7 +10,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
-	"github.com/mattermost/mattermost-server/v5/model"
+	"github.com/mattermost/mattermost-server/v6/model"
 )
 
 func TestComparePassword(t *testing.T) {

services/users/profile_picture.go

@@ -18,9 +18,9 @@ import (
 
 	"github.com/golang/freetype"
 	"github.com/golang/freetype/truetype"
-	"github.com/mattermost/mattermost-server/v5/model"
-	"github.com/mattermost/mattermost-server/v5/shared/filestore"
-	"github.com/mattermost/mattermost-server/v5/utils/fileutils"
+	"github.com/mattermost/mattermost-server/v6/model"
+	"github.com/mattermost/mattermost-server/v6/shared/filestore"
+	"github.com/mattermost/mattermost-server/v6/utils/fileutils"
 )
 
 const (

services/users/service.go

@@ -9,10 +9,10 @@ import (
 	"runtime"
 	"sync"
 
-	"github.com/mattermost/mattermost-server/v5/einterfaces"
-	"github.com/mattermost/mattermost-server/v5/model"
-	"github.com/mattermost/mattermost-server/v5/services/cache"
-	"github.com/mattermost/mattermost-server/v5/store"
+	"github.com/mattermost/mattermost-server/v6/einterfaces"
+	"github.com/mattermost/mattermost-server/v6/model"
+	"github.com/mattermost/mattermost-server/v6/services/cache"
+	"github.com/mattermost/mattermost-server/v6/store"
 )
 
 type UserService struct {

services/users/service_test.go

@@ -6,7 +6,7 @@ package users
 import (
 	"testing"
 
-	"github.com/mattermost/mattermost-server/v5/model"
+	"github.com/mattermost/mattermost-server/v6/model"
 	"github.com/stretchr/testify/require"
 )
 

services/users/session.go

@@ -8,9 +8,9 @@ import (
 	"fmt"
 	"time"
 
-	"github.com/mattermost/mattermost-server/v5/model"
-	"github.com/mattermost/mattermost-server/v5/shared/mlog"
-	"github.com/mattermost/mattermost-server/v5/store/sqlstore"
+	"github.com/mattermost/mattermost-server/v6/model"
+	"github.com/mattermost/mattermost-server/v6/shared/mlog"
+	"github.com/mattermost/mattermost-server/v6/store/sqlstore"
 	"github.com/pkg/errors"
 )
 

services/users/session_test.go

@@ -7,7 +7,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/mattermost/mattermost-server/v5/model"
+	"github.com/mattermost/mattermost-server/v6/model"
 	"github.com/stretchr/testify/require"
 )
 

services/users/users.go

@@ -8,11 +8,11 @@ import (
 	"encoding/base64"
 	"fmt"
 
-	"github.com/mattermost/mattermost-server/v5/model"
-	"github.com/mattermost/mattermost-server/v5/shared/i18n"
-	"github.com/mattermost/mattermost-server/v5/shared/mfa"
-	"github.com/mattermost/mattermost-server/v5/shared/mlog"
-	"github.com/mattermost/mattermost-server/v5/store"
+	"github.com/mattermost/mattermost-server/v6/model"
+	"github.com/mattermost/mattermost-server/v6/shared/i18n"
+	"github.com/mattermost/mattermost-server/v6/shared/mfa"
+	"github.com/mattermost/mattermost-server/v6/shared/mlog"
+	"github.com/mattermost/mattermost-server/v6/store"
 )
 
 type UserCreateOptions struct {

services/users/utils.go

@@ -6,7 +6,7 @@ package users
 import (
 	"strings"
 
-	"github.com/mattermost/mattermost-server/v5/model"
+	"github.com/mattermost/mattermost-server/v6/model"
 )
 
 func maxInt(a, b int) int {