MM-53032: Fix module path after repo rename (#23689)

It was a good decision in hindsight to keep the public module as 0.x
because this would have been a breaking change again.

https://mattermost.atlassian.net/browse/MM-53032
```release-note
Changed the Go module path from github.com/mattermost/mattermost-server/server/v8 to github.com/mattermost/mattermost/server/v8.

For the public facing module, it's path is also changed from github.com/mattermost/mattermost-server/server/public to github.com/mattermost/mattermost/server/public
```

server/channels/app/session.go

@@ -10,12 +10,12 @@ import (
 	"net/http"
 	"os"
 
-	"github.com/mattermost/mattermost-server/server/public/model"
-	"github.com/mattermost/mattermost-server/server/public/shared/mlog"
-	"github.com/mattermost/mattermost-server/server/v8/channels/app/platform"
-	"github.com/mattermost/mattermost-server/server/v8/channels/app/users"
-	"github.com/mattermost/mattermost-server/server/v8/channels/audit"
-	"github.com/mattermost/mattermost-server/server/v8/channels/store"
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/public/shared/mlog"
+	"github.com/mattermost/mattermost/server/v8/channels/app/platform"
+	"github.com/mattermost/mattermost/server/v8/channels/app/users"
+	"github.com/mattermost/mattermost/server/v8/channels/audit"
+	"github.com/mattermost/mattermost/server/v8/channels/store"
 )
 
 func (a *App) CreateSession(session *model.Session) (*model.Session, *model.AppError) {