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
```

imports/placeholder.go

@@ -5,35 +5,35 @@ package imports
 
 import (
 	// This is a placeholder so this package can be imported in Team Edition when it will be otherwise empty.
-	_ "github.com/mattermost/mattermost-server/v5/migrations"
+	_ "github.com/mattermost/mattermost-server/v6/migrations"
 
 	// This is a placeholder so this package can be imported in Team Edition when it will be otherwise empty.
-	_ "github.com/mattermost/mattermost-server/v5/plugin/scheduler"
+	_ "github.com/mattermost/mattermost-server/v6/plugin/scheduler"
 
 	// This is a placeholder so this package can be imported in Team Edition when it will be otherwise empty.
-	_ "github.com/mattermost/mattermost-server/v5/services/searchengine/bleveengine/indexer"
+	_ "github.com/mattermost/mattermost-server/v6/services/searchengine/bleveengine/indexer"
 
 	// This is a placeholder so this package can be imported in Team Edition when it will be otherwise empty.
-	_ "github.com/mattermost/mattermost-server/v5/jobs/expirynotify"
+	_ "github.com/mattermost/mattermost-server/v6/jobs/expirynotify"
 
 	// This is a placeholder so this package can be imported in Team Edition when it will be otherwise empty.
-	_ "github.com/mattermost/mattermost-server/v5/jobs/active_users"
+	_ "github.com/mattermost/mattermost-server/v6/jobs/active_users"
 
 	// This is a placeholder so this package can be imported in Team Edition when it will be otherwise empty.
-	_ "github.com/mattermost/mattermost-server/v5/jobs/product_notices"
+	_ "github.com/mattermost/mattermost-server/v6/jobs/product_notices"
 
 	// This is a placeholder so this package can be imported in Team Edition when it will be otherwise empty.
-	_ "github.com/mattermost/mattermost-server/v5/jobs/import_process"
+	_ "github.com/mattermost/mattermost-server/v6/jobs/import_process"
 
 	// This is a placeholder so this package can be imported in Team Edition when it will be otherwise empty.
-	_ "github.com/mattermost/mattermost-server/v5/jobs/import_delete"
+	_ "github.com/mattermost/mattermost-server/v6/jobs/import_delete"
 
 	// This is a placeholder so this package can be imported in Team Edition when it will be otherwise empty.
-	_ "github.com/mattermost/mattermost-server/v5/jobs/export_process"
+	_ "github.com/mattermost/mattermost-server/v6/jobs/export_process"
 
 	// This is a placeholder so this package can be imported in Team Edition when it will be otherwise empty.
-	_ "github.com/mattermost/mattermost-server/v5/jobs/export_delete"
+	_ "github.com/mattermost/mattermost-server/v6/jobs/export_delete"
 
 	// This is a placeholder so this package can be imported in Team Edition when it will be otherwise empty.
-	_ "github.com/mattermost/mattermost-server/v5/jobs/resend_invitation_email"
+	_ "github.com/mattermost/mattermost-server/v6/jobs/resend_invitation_email"
 )