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
```

wsapi/api.go

@@ -4,7 +4,7 @@
 package wsapi
 
 import (
-	"github.com/mattermost/mattermost-server/v5/app"
+	"github.com/mattermost/mattermost-server/v6/app"
 )
 
 type API struct {

wsapi/status.go

@@ -4,8 +4,8 @@
 package wsapi
 
 import (
-	"github.com/mattermost/mattermost-server/v5/model"
-	"github.com/mattermost/mattermost-server/v5/shared/mlog"
+	"github.com/mattermost/mattermost-server/v6/model"
+	"github.com/mattermost/mattermost-server/v6/shared/mlog"
 )
 
 func (api *API) InitStatus() {

wsapi/system.go

@@ -4,7 +4,7 @@
 package wsapi
 
 import (
-	"github.com/mattermost/mattermost-server/v5/model"
+	"github.com/mattermost/mattermost-server/v6/model"
 )
 
 func (api *API) InitSystem() {

wsapi/user.go

@@ -4,7 +4,7 @@
 package wsapi
 
 import (
-	"github.com/mattermost/mattermost-server/v5/model"
+	"github.com/mattermost/mattermost-server/v6/model"
 )
 
 func (api *API) InitUser() {

wsapi/websocket_handler.go

@@ -6,10 +6,10 @@ package wsapi
 import (
 	"net/http"
 
-	"github.com/mattermost/mattermost-server/v5/app"
-	"github.com/mattermost/mattermost-server/v5/model"
-	"github.com/mattermost/mattermost-server/v5/shared/i18n"
-	"github.com/mattermost/mattermost-server/v5/shared/mlog"
+	"github.com/mattermost/mattermost-server/v6/app"
+	"github.com/mattermost/mattermost-server/v6/model"
+	"github.com/mattermost/mattermost-server/v6/shared/i18n"
+	"github.com/mattermost/mattermost-server/v6/shared/mlog"
 )
 
 func (api *API) ApiWebSocketHandler(wh func(*model.WebSocketRequest) (map[string]interface{}, *model.AppError)) webSocketHandler {