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/testlib/cluster.go

@@ -6,8 +6,8 @@ package testlib
 import (
 	"sync"
 
-	"github.com/mattermost/mattermost-server/server/public/model"
-	"github.com/mattermost/mattermost-server/server/v8/einterfaces"
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/v8/einterfaces"
 )
 
 type FakeClusterInterface struct {

server/channels/testlib/helper.go

@@ -13,13 +13,13 @@ import (
 
 	"github.com/pkg/errors"
 
-	"github.com/mattermost/mattermost-server/server/public/model"
-	"github.com/mattermost/mattermost-server/server/v8/channels/store"
-	"github.com/mattermost/mattermost-server/server/v8/channels/store/searchlayer"
-	"github.com/mattermost/mattermost-server/server/v8/channels/store/sqlstore"
-	"github.com/mattermost/mattermost-server/server/v8/channels/store/storetest"
-	"github.com/mattermost/mattermost-server/server/v8/channels/utils"
-	"github.com/mattermost/mattermost-server/server/v8/platform/services/searchengine"
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/v8/channels/store"
+	"github.com/mattermost/mattermost/server/v8/channels/store/searchlayer"
+	"github.com/mattermost/mattermost/server/v8/channels/store/sqlstore"
+	"github.com/mattermost/mattermost/server/v8/channels/store/storetest"
+	"github.com/mattermost/mattermost/server/v8/channels/utils"
+	"github.com/mattermost/mattermost/server/v8/platform/services/searchengine"
 )
 
 type MainHelper struct {

server/channels/testlib/resources.go

@@ -12,10 +12,10 @@ import (
 
 	"github.com/pkg/errors"
 
-	"github.com/mattermost/mattermost-server/server/public/model"
-	"github.com/mattermost/mattermost-server/server/public/utils"
-	"github.com/mattermost/mattermost-server/server/v8/channels/utils/fileutils"
-	"github.com/mattermost/mattermost-server/server/v8/platform/shared/filestore"
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/public/utils"
+	"github.com/mattermost/mattermost/server/v8/channels/utils/fileutils"
+	"github.com/mattermost/mattermost/server/v8/platform/shared/filestore"
 )
 
 const (

server/channels/testlib/store.go

@@ -7,10 +7,10 @@ import (
 	"net/http"
 	"strconv"
 
-	"github.com/mattermost/mattermost-server/server/public/model"
-	"github.com/mattermost/mattermost-server/server/public/plugin/plugintest/mock"
-	"github.com/mattermost/mattermost-server/server/v8/channels/store"
-	"github.com/mattermost/mattermost-server/server/v8/channels/store/storetest/mocks"
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/public/plugin/plugintest/mock"
+	"github.com/mattermost/mattermost/server/v8/channels/store"
+	"github.com/mattermost/mattermost/server/v8/channels/store/storetest/mocks"
 )
 
 type TestStore struct {